Arandell Corporation v. Xcel Energy Inc .

In the
United States Court of Appeals
For the Seventh Circuit
____________________
No. 22-3279
A RANDELL C ORPORATION , et al.,
Plaintiffs-Appellees,
v.
X CEL ENERGY I NC ., et al.,
Defendants-Appellants.
____________________
Appeal from the United States District Court for the
Western District of Wisconsin.
Nos. 3:07-cv-00076 & 3:09-cv-00240 — James D. Peterson, Chief Judge.
____________________
A RGUED A PRIL 5, 2023 — DECIDED A UGUST 5, 2025
____________________
Before S YKES , Chief Judge, and H AMILTON and BRENNAN ,
Circuit Judges.
HAMILTON , Circuit Judge. This interlocutory appeal
challenges certification of a statewide plaintiff class in a price-
fixing case brought under Wisconsin law. The case arises from
a broad conspiracy to manipulate natural gas prices from 2000
to 2002. The central issue is whether common issues
predominate over individual issues under Federal Rule of
Civil Procedure 23(b)(3) so that class certification is

-- 1 of 30 --

2 No. 22-3279
appropriate. To be more precise, the question here is whether
the district court had a sound basis for answering that
question “yes” without addressing in more detail the
conflicting expert testimony on the issue of antitrust impact.
It is well recognized that price fixing causes antitrust injury
within the meaning of Brunswick Corp. v. Pueblo Bowl-O-Mat,
Inc., 429 U.S. 477, 4888 (1977) (plaintiffs could not recover
damages for alleged antitrust violation on theory that
violation enabled more competitors to survive in relevant
market); see generally Robert H. Bork, The Antitrust Paradox
67 (1978) (“The per se rule against naked price fixing and
similar agreements not to compete is the oldest and clearest
of antitrust doctrines, and its existence can be explained only
by a preference for consumer welfare as the exclusive goal of
antitrust.”). Higher fixed prices are the result of the illegal
conduct. In this case, therefore, the question of antitrust
impact is primarily an issue of causation and the scope of the
geographic market. As we explain below, while that issue
overlaps substantially with the merits of plaintiffs’ claims,
that overlap does not allow the district court to postpone
dealing with the issue at the class certification stage.
The existence of a conspiracy here has been proven in
other proceedings. The existence and scope of the alleged con-
spiracy are certainly subject to common proof. It is also well
established that individual questions of damages should not
defeat class certification. The pivotal question here is whether
plaintiffs can use common proof to show antitrust impact
from the conspiracy. That will depend on whether they can
show the existence of a national market such that defendants’
conspiracy to manipulate prices affected the prices plaintiffs
paid for gas in Wisconsin. As a general rule, class certification
is common in price-fixing cases, see 7AA Wright & Miller,

-- 2 of 30 --

No. 22-3279 3
Federal Practice & Procedure § 1781 & n.22 (3d. ed. 2025), par-
ticularly where the product involved is a fungible commodity
like gas. See Messner v. Northshore University HealthSystem, 669
F.3d 802, 816 (7th Cir. 2012) (showing antitrust impact of
price-fixing is relatively simple in market for generic com-
modity). Nevertheless, defendants have offered evidence that
they contend shows that natural gas price markets were so
complex and unusual as to prevent such common proof.
Plaintiffs’ economic experts have responded with detailed re-
buttals.
The district court deferred full engagement with those de-
bates at the class certification stage, leaving further consider-
ation for the merits of the case. In light of recent decisions by
the Supreme Court and this court, however, we conclude that
the district court needed to engage more fully with the con-
flicting expert evidence to decide on class certification. While
we would not be surprised if the case turns out to be proper
for class certification—this is after all a price-fixing case in-
volving a fungible commodity traded across a nationwide
network of pipelines—we must vacate the certification and re-
mand for further consideration of expert disputes.
I. Factual Background
A. The Market for Natural Gas
Natural gas is a fungible commodity. One molecule is in-
distinguishable from another. It is transported around the
United States by a nationwide network of pipelines. Most
consumers of natural gas in the United States are individuals
and small businesses who buy gas from local utilities. Arandell
Corp. v. Centerpoint Energy Services, Inc., 900 F.3d 623, 625–26
(9th Cir. 2018) (earlier appeal reversing denial of class

-- 3 of 30 --

4 No. 22-3279
certification in larger multidistrict litigation). But larger con-
sumers, including this case’s plaintiffs, contract to buy large
volumes of gas directly from the gas companies themselves or
through intermediaries. Different pricing arrangements are
common, including fixed-price contracts and contracts with
variable prices tied to an index. Contract durations also vary.
At the relevant time, gas companies would report their
sales to trade publications, such as Inside FERC, Gas Daily, and
NYMEX. Those trade publications used that data to publish
index prices that would directly affect some contract prices
tied to those indices. Fixed-price contracts were also affected,
as buyers and sellers negotiated with the index price as a
benchmark. See Arandell, 900 F.3d at 626 & n.1.
B. The Manipulation of the Market
In the early 2000s, natural gas prices climbed “to extraor-
dinary levels.” Oneok, Inc. v. Learjet, Inc., 575 U.S. 373, 382
(2015) (internal quotations omitted), quoting FERC, Final Re-
port on Price Manipulation in Western Markets: Fact-Finding In-
vestigation of Potential Manipulation of Electric and Natural Gas
Prices (hereafter “FERC Report”) at ES-1 (Mar. 2003)
(https://perma.cc/55SP-F8ST). The Federal Energy Regulatory
Commission (FERC) investigated and uncovered tell-tale
signs of market manipulation: churning, wash trading, and
false reporting. See FERC Report at ES-5, ES-11, & I-18.
“Churning” refers to buying and selling gas during the
same trading interval such that the trades offset each other.
Arandell, 900 F.3d at 626 n.3. “Wash trading” refers to
arranging a “pair of trades of the same good between the
same parties, involving no economic risk and no net change
in beneficial ownership.” Id. at n.2 (internal quotation marks

-- 4 of 30 --

No. 22-3279 5
omitted). “False reporting” refers to reporting such churning,
wash trading, and other fabricated trading data to the trade
publications that set the index price. Id. at 626–27.
Unknown to outside observers, this conduct masqueraded
as legitimate market activity. But as known by many inside
the industry, according to plaintiffs, these tactics among com-
petitors really amounted to mechanisms to fix prices. FERC’s
investigation concluded that these price increases were driven
by some of the nation’s largest natural gas conglomerates, in-
cluding Enron and defendants in this case. Id. at 626.
These practices can function as covert mechanisms for
price-fixing. By engaging in churning and wash trading,
market participants can report what amount to fictional
prices, creating the illusion of supply and demand dynamics
that do not actually exist. A higher trading volume signals a
higher demand for natural gas and vice versa. When this
trading data was reported to price index publishers, it
artificially inflated—or at times deflated—the benchmark
prices used to set rates in many natural gas contracts. In doing
so, competitors were not simply engaging in misleading
conduct; they were collectively manipulating the market to
produce prices that would not have applied under
competitive conditions.
C. Penalties and Remedies for Manipulating the Market
The defendants’ conduct attracted attention from FERC,
the Securities and Exchange Commission, the Commodities
Futures Trading Commission, and the Department of Justice,
leading to government investigations, administrative orders,
and criminal indictments. Those proceedings resulted in civil
penalties, criminal convictions, prison sentences, and heavy

-- 5 of 30 --

6 No. 22-3279
financial sanctions. This case is a slice of the private civil liti-
gation over the market manipulation. The point is that the
price-fixing conspiracy here was not merely alleged. That
does not mean the extent of the conspiracy has been deter-
mined, but its existence has been proven again and again.
Horizontal price-fixing violates both federal and
Wisconsin antitrust law under the Sherman Act, 15 U.S.C. § 1,
and Wis. Stat. § 133.03. The Wisconsin Supreme Court has
long made clear that federal interpretations of the Sherman
Act should guide interpretation of the Wisconsin Act. E.g.,
Conley Publishing Group Ltd. v. Journal Communications, Inc.,
2003 WI 119, ¶ 17, 265 Wis. 2d 128, 140–41, 665 N.W.2d 879,
885–86, abrogated on other grounds, Olstad v. Microsoft Corp.,
2005 WI 121, ¶ 74, 284 Wis. 2d 224, 259, 700 N.W.2d 139, 156;
State v. Waste Management of Wisconsin, Inc., 261 N.W.2d 147,
153 n.12 (Wis. 1978); City of Madison v. Hyland, Hall & Co., 243
N.W.2d 422, 428–29 (Wis. 1976). The state law closely tracks
the language of the federal law as to the conduct prohibited.
There are important differences, however, in the available
civil remedies.
Under Wisconsin law, if a contract has been made by a
party while it is a member of a combination or conspiracy out-
lawed under § 133.03 and the contract is connected with the
violation, the contract “shall be void.” Wis. Stat. § 133.14. A
party who made a payment under the contract may recover
“any payment” made under the contract from any person
who received or benefited from such payment. Id. This “full
consideration” remedy is not available under federal antitrust
law. It appears to have been designed by the Wisconsin legis-
lature to offer a streamlined and relatively simple remedy.

-- 6 of 30 --

No. 22-3279 7
Federal law offers a treble-damage civil remedy for anti-
trust violations, 15 U.S.C. § 15(a), and Wisconsin also offers a
treble-damage remedy as a supplement or alternative to the
“full consideration” remedy, Wis. Stat. § 133.18(1)(a). Federal
law limits that remedy to direct purchasers from violators; in-
direct purchasers may not recover damages. Illinois Brick Co.
v. Illinois, 431 U.S. 720, 746–47 (1977). But Wisconsin wrote its
antitrust law to reject the federal Illinois Brick doctrine, ex-
pressly permitting suit by “any person injured, directly or in-
directly.” Olstad, 700 N.W.2d 139, ¶61 (alteration omitted), cit-
ing Wis. Stat. § 133.18.
II. Procedural Background
A. Allegations of an Antitrust Conspiracy
Numerous plaintiffs—industrial and commercial pur-
chasers of natural gas—sued the defendant gas companies, al-
leging that the plaintiffs paid higher gas prices because each
defendant participated in a price-fixing conspiracy. Under 28
U.S.C. § 1407, various actions around the country were trans-
ferred to the District of Nevada under a multidistrict litigation
docket for consolidated pretrial proceedings. The cases in-
cluded actions on behalf of class members in Kansas, Mis-
souri, Colorado, and Wisconsin. In re Western States Wholesale
Natural Gas Antitrust Litig., MDL No. 1566, 2017 WL 1243135,
at *10–14 (D. Nev. Mar. 30, 2017) (denying class certification
in several cases, including this Wisconsin case), vacated and
remanded, 743 F. App’x 825, 828–30 (9th Cir. 2018). After re-
mand from the Ninth Circuit, the MDL transferee court re-
turned this Wisconsin case to the originating court, the West-
ern District of Wisconsin. After nearly twenty years of litiga-
tion, we are still dealing with the threshold issue of class cer-
tification.

-- 7 of 30 --

8 No. 22-3279
The Wisconsin plaintiffs in this case assert antitrust claims
under only Wisconsin antitrust law, not federal antitrust law.
See Wis. Stat. § 133.01 et seq. They pursue both the “full
consideration” remedy under § 133.14 and treble damages
under § 133.18(1)(a).
B. The Expert Disputes
After transfer back to the Western District of Wisconsin,
the Wisconsin plaintiffs moved again to certify the same Rule
23(b)(3) class of industrial and commercial purchasers of
natural gas for their own use or consumption in Wisconsin
from January 1, 2000, to October 21, 2002, excluding certain
other purchasers. The plaintiffs proposed common questions
of law and fact, including whether the defendants conspired
to manipulate the price of natural gas through wash trading,
churning, and false reporting; whether the class paid higher
prices for natural gas as a result; the method to determine the
determine recovery for full consideration; and the method to
determine recovery for treble damages. In support, the
plaintiffs relied on the same expert evidence providing
economic models to calculate antitrust impact and actual
damages for the treble damage remedy. This expert evidence
is the focus of this appeal regarding whether the expert
models established predominance.
The plaintiffs’ experts, Dr. Michael Harris and Dr. Mark
Dwyer, began by describing the nature of the natural gas
market. Natural gas, they explained, is a fungible commodity
sold at standardized prices and transported through a
nationwide network of pipelines. R.208-18 at 28, ¶ 59. The
natural gas market is nationwide, as shown by tightly
correlated prices from region to region and index to index.
R.208-12 at 26, ¶ 59; R.208-13 at 14 ¶ 34. Given these market

-- 8 of 30 --

No. 22-3279 9
fundamentals, they explained that “it can reasonably be
concluded every area of the country was impacted by the
manipulation.” R.208-12 at 9, ¶ 17. In that regard, the
plaintiffs sought to measure impact and damages with
regression models and a “but-for price index.” R.208-12 at 28.
That is, the experts calculated what they believe the index
prices would have been without the conduct of the
defendants and non-defendant co-conspirators. After
controlling for location and price type, the plaintiffs’ experts
concluded that “all, or nearly all of the class members in
Wisconsin were impacted by Defendants’ conduct.” R.208-12
at 39, ¶ 79.
The defendants’ experts, Dr. Michelle Burtis and Dr. Ran-
dall Heeb, raised numerous objections to plaintiffs’ experts’
opinion. See Dkt. 213-1 & 213-3 (Burtis); Dkt. 213-4 (Heeb).
They opined that the plaintiffs’ models fail to prove a single,
interrelated market for natural gas, fail to account for varieties
in contract terms and data indicating manipulated prices
sometimes fell, and in other ways do not evaluate or sample
the correct data. R.210 at 30.
Plaintiffs’ experts, Dr. Harris and Dr. Dwyer, responded
to these criticisms with detailed rebuttal reports. Dkt. 225-6,
225-9, & 225-12. They argued that the defense experts had, in
essence, raised a number of red herrings to try to complicate
and obscure what is at bottom a fairly straightforward price-
fixing case involving a fungible commodity in a national mar-
ket. Indeed, among price-fixing defendants in fungible com-
modity cases, such efforts to defeat class certification by fo-
cusing on varieties of related products and contracts appear
to be quite common. See, e.g., Kleen Products LLC v. Int’l Paper
Co., 831 F.3d 919, 927–29 (7th Cir. 2016) (affirming certification

-- 9 of 30 --

10 No. 22-3279
of nationwide plaintiff class in containerboard price-fixing
case relying on opinions of Dr. Harris and Dr. Dwyer to show
antitrust impact); In re Ready-Mix Concrete Antitrust Litig., 261
F.R.D. 154, 170–72 (S.D. Ind. 2009) (variations in concrete
products did not defeat class certification in regional price-
fixing class action); In re Bromine Antitrust Litig., 203 F.R.D.
403, 414–15 (S.D. Ind. 2001) (same in nationwide price-fixing
case for bromine products); In re Auction Houses Antitrust
Litig., 193 F.R.D. 162, 166–67 & n.13 (S.D.N.Y. 2000) (same in
nationwide price-fixing case for auction services: “Price fixing
conspiracies, at least to the extent they succeed in fixing
prices, almost invariably injure everyone who purchases the
relevant goods or services. Defendants appear greatly to ex-
aggerate the extent to which individualized proof of impact
may be required.”) (footnote omitted); In re Industrial Dia-
monds Antitrust Litig., 167 F.R.D. 374, 383 (S.D.N.Y. 1996)
(same in nationwide price-fixing case for industrial diamond
products); In re Linerboard Antitrust Litig., 203 F.R.D. 197, 216–
20 (E.D. Pa. 2001) (certifying nationwide classes in case alleg-
ing conspiracy to restrict output of linerboard), aff’d, 305 F.3d
145 (3d Cir. 2002).
C. The Class Certification Order
Judge Conley, to whom the case was originally assigned,
agreed with the defendants that although “these experts’
opinions are admissible, [that] does not mean plaintiffs have
established the existence of a common method of proof.”
Arandell Corp. v. Xcel Energy, Inc., No. 07-CV-076-WMC, 2022
WL 2314717, at *9 (W.D. Wis. June 28, 2022). The court
continued: “the finding that these experts are qualified to
render an opinion that is sufficiently reliable and will aid in
the jury’s determinations may well support a finding that

-- 10 of 30 --

No. 22-3279 11
plaintiffs have presented a credible theory for pursuing their
claims on behalf of a larger class.” Id. Judge Conley found that
whether a conspiracy to raise prices existed and whether there
was a nationwide market susceptible to such a conspiracy
were common questions subject to common proof. This
finding supported the court’s finding of predominance:
“Given the significant issues that can be resolved at the class
level based on plaintiffs’ theory of liability and the evidence of
a single, nationwide natural gas market due to defendants’
allegedly illicit actions, the court concludes that the
predominance requirement is satisfied.” Id. at *12. Judge
Conley acknowledged that the defendants “point[ed] to
differences between both the plaintiffs and defendants,” but
he did not expressly address or make findings about the
defense arguments that the plaintiffs’ models were
inadequate so as to defeat predominance. Id. at *10.
Judge Conley certified the proposed plaintiff class but
soon after that recused from further proceedings in the case.
Chief Judge Peterson, to whom the case was reassigned,
quickly denied the defendants’ motion to vacate the class cer-
tification but encouraged this interlocutory appeal. We
granted leave to appeal class certification under Federal Rule
of Civil Procedure 23(f), limiting the interlocutory appeal to
“whether the district court properly assessed the parties’ ex-
pert opinions when deciding the motion to certify.” We re-
view a class certification order for an abuse of discretion,
which can include reviewing whether a district court commit-
ted a legal error by conducting an insufficiently “rigorous
analysis.” Santiago v. City of Chicago, 19 F.4th 1010, 1016 (7th
Cir. 2021).

-- 11 of 30 --

12 No. 22-3279
III. Class Certification, Rigorous Analysis, and Resolving Expert
Disputes
A. Requirements for Class Certification
The basics of class certification are not disputed here. To
be certified, a proposed class must first meet “the Rule 23(a)
requirements of numerosity, typicality, commonality, and ad-
equacy of representation.” Messner, 669 F.3d at 811. The dis-
trict court found all four requirements under Rule 23(a) were
met here, and there is no dispute about them on appeal. The
class must then fit into one of three categories under Rule
23(b). To certify a plaintiff class seeking damages under Rule
23(b)(3), as plaintiffs seek here, “a court must find ‘that the
questions of law or fact common to class members predomi-
nate over any questions affecting only individual members
….” Fed. R. Civ. P. 23(b)(3).
A common question is one where “the same evidence will
suffice for each member to make a prima facie showing [or]
the issue is susceptible to generalized, class-wide proof.” Ty-
son Foods, Inc. v. Bouaphakeo, 577 U.S. 442, 453 (2016) (internal
quotations omitted), quoting 2 W. Rubenstein, Newberg on
Class Actions § 4:50, p. 196 (5th ed. 2012). An individual ques-
tion is one where “’members of a proposed class will need to
present evidence that varies from member to member.’” Id.,
quoting Rubenstein, supra, § 4:50, p. 196. To determine which
questions are common versus individual, the district court
must circumscribe the claims and break them down into their
constituent elements. Santiago, 19 F.4th at 1018. In so doing,
the district court must separately analyze the claims “to better
understand the relationship between each claim’s common
and individual questions.” Eddlemon v. Bradley University, 65
F.4th 335, 339–40 (7th Cir. 2023).

-- 12 of 30 --

No. 22-3279 13
With common and individual questions identified, the
district court must determine whether common questions
predominate. Predominance is a “qualitative rather than
quantitative concept.” Parko v. Shell Oil Co., 739 F.3d 1083,
1085 (7th Cir. 2014). “There is no mathematical or mechanical
test for evaluating predominance.” Messner, 559 F.3d at 814. It
is not determined “simply by counting noses: that is, deter-
mining whether there are more common issues or more indi-
vidual issues….” Parko, 739 F.3d at 1085. More than a “tally of
common questions,” the district court must “give careful
scrutiny to the relation between common and individual
questions in a case,” and “consider their relative importance.”
Tyson, 577 U.S. at 453 (second quotation); Santiago, 19 F.4th at
1016 (first and third quotations); accord, 2 Rubenstein, New-
berg on Class Actions § 4:51, pp. 198–200.
B. “Rigorous Analysis” and the Delicate Balance
The trial court can certify a class only if it is “’satisfied, af-
ter a rigorous analysis, that the prerequisites’ for class certifi-
cation have been met.” Bell v. PNC Bank, N.A., 800 F.3d 360,
373 (7th Cir. 2015), quoting CE Design Ltd. v. King Architectural
Metals, Inc., 637 F.3d 721, 723 (7th Cir. 2011). The Supreme
Court has made it clear that class certification imposes more
than a pleading standard. Wal-Mart Stores, Inc. v. Dukes, 564
U.S. 338, 350 (2011). “The party seeking certification bears the
burden of demonstrating that certification is proper by a pre-
ponderance of the evidence.” Bell, 800 F.3d at 373.
At the same time, the Supreme Court has long cautioned
lower courts to focus on the requirements of Rule 23 and not
to “conduct a preliminary inquiry into the merits of a suit in
order to determine whether it may be maintained as a class
action.” Eisen v. Carlisle & Jacquelin, 417 U.S. 156, 177 (1974).

-- 13 of 30 --

14 No. 22-3279
The Eisen principle does not mean, however, that there is a
solid wall between class certification and the merits, as more
recent cases have made clear. The Court has recognized that
there will often be some overlap between class issues and
merits. The overlap does not allow a district court to skip over
an issue critical to certification just because it overlaps with
the merits. See Goldman Sachs Group, Inc. v. Arkansas Teacher
Retirement System, 594 U.S. 113, 122 (2021) (issue of price
impact in securities fraud cases), citing In re Allstate Corp.
Securities Litig., 966 F.3d 595, 613 n.6 (7th Cir. 2020); see
generally Amgen Inc. v. Connecticut Retirement Plans and Trust
Funds, 568 U.S. 455, 466 (2013) (securities fraud: “Rule 23
grants courts no license to engage in free-ranging merits
inquiries at the certification stage. Merits questions may be
considered to the extent—but only to the extent—that they are
relevant to determining whether the Rule 23 prerequisites for
class certification are satisfied.”); Halliburton Co. v. Erica P.
John Fund, Inc., 573 U.S. 258, 283 (2014) (securities fraud: price
impact “has everything to do with the issue of predominance
at the class certification stage”); Dukes, 564 U.S. at 351–52
(noting necessity of touching on merits issues in employment
discrimination class certification: “The necessity of touching
aspects of the merits in order to resolve preliminary matters,
e.g., jurisdiction and venue, is a familiar feature of
litigation.”); General Telephone Co. of Southwest v. Falcon, 457
U.S. 147, 161 (1982) (“rigorous analysis” required under Rule
23).
This general principle applies to antitrust cases. Comcast
Corp. v. Behrend, 569 U.S. 27, 34–35 (2013) (reversing class cer-
tification where lower courts refused to entertain challenges
to plaintiffs’ damages model as undermining predominance
of common issues; overlap with merits did not justify refusal

-- 14 of 30 --

No. 22-3279 15
to engage with defense evidence and arguments); In re Hydro-
gen Peroxide Antitrust Litig., 552 F.3d 305, 322–25 (3d Cir. 2008)
(vacating class certification where district court relied on ad-
missibility of plaintiffs’ expert evidence but did not engage
with evidence to resolve relevant disputes with defense ex-
perts).
We have noted before that the Supreme Court’s teachings
call for district judges to perform a careful balancing act. See
Allstate, 966 F.3d at 603 (securities fraud). In conducting its
rigorous analysis, the court is not permitted to turn the class
certification proceedings into a “dress rehearsal for the trial
on the merits.” Messner, 669 F.3d at 811. “[C]ertification is
largely independent of the merits … and a certified class can
go down in flames on the merits.” Schleicher v. Wendt, 618 F.3d
679, 685 (7th Cir. 2010). The trial court is not permitted to re-
solve disputed issues that affect only the merits. A court is
permitted to “‘take a peek at the merits before certifying a
class,’ but the peek must be ‘limited to those aspects of the
merits that affect the decisions essential under Rule 23.’”
Messner, 669 F.3d at 823–24, quoting Schleicher, 618 F.3d at 685.
As we will see, this appeal involves much more than a “peek,”
but the work must still be done.
In the face of material disputes bearing on class certifica-
tion, the trial court must receive evidence, whether by affida-
vit, evidentiary hearings, or otherwise, and then resolve the
disputes or choose between competing perspectives. West v.
Prudential Securities, Inc., 282 F.3d 935, 938 (7th Cir. 2002) (re-
versing class certification when court did not address dispos-
itive merits issue at certification stage); Szabo v. Bridgeport Ma-
chines, Inc., 249 F.3d 672, 676 (7th Cir. 2001) (vacating and re-
manding class certification; district court must make

-- 15 of 30 --

16 No. 22-3279
“whatever factual and legal inquiries are necessary under
Rule 23). The trial court must do its best to maintain a delicate
balance “between evaluating evidence to determine whether
a common question exists and predominates, without weigh-
ing that evidence to determine whether the plaintiff class will
ultimately prevail on the merits.” Bell, 800 F.3d at 377. But the
trial court is not permitted to “duck hard questions by observ-
ing that each side has some support, or that considerations
relevant to class certification also may affect the decision on
the merits. Tough questions must be faced and squarely de-
cided …,” even if the dispute regards expert evidence. West,
282 F.3d at 938.
C. Resolving Expert Disputes
As the district court recognized here, in the context of ex-
pert evidence, Rule 23’s “rigorous analysis” requirement for
class certification is not the same as the test for admissibility
under Federal Rule of Evidence 702 and Daubert v. Merrell
Dow Pharmaceuticals, Inc., 509 U.S. 579 (1993), and its progeny.
Expert evidence can be admissible under Rule 702 and Daub-
ert but still fall short of proving the Rule 23 requirements for
class certification. Comcast, 569 U.S. at 32–33, n.4 (distinguish-
ing between admissibility and adequacy of evidence). In other
words, just because expert evidence is admissible does not
mean that it will justify class certification.
At class certification, a district court is not required to re-
solve every expert dispute. A court is neither required nor
permitted at the class stage to resolve disputes on the merits
unrelated to the decisions essential to Rule 23. However,
where the defendants have offered admissible evidence that,
if credited, would mean individual questions would predom-
inate over common questions, then the district court must

-- 16 of 30 --

No. 22-3279 17
“investigate[ ] the realism” of the expert evidence “in light of
the defendants’ counterarguments,” and take evidence to that
end. Parko, 739 F.3d at 1086. Otherwise, any party would be
able to obtain (or defeat) class certification “just by hiring a
competent expert.” West, 282 F.3d at 938.
Plaintiffs defend the district court’s decision by arguing
that at trial they will have to prove a nationwide market as
part of their merits case. Their core evidence on that issue will
come from Dr. Harris and Dr. Dryer, and defendants’ core ev-
idence on that issue will come from Dr. Burtis and Dr. Heeb.
Plaintiffs say that, win or lose at trial, the relevant evidence
will be common to all class members. We have pointed out
that common evidence does not mean a class will win; the
class can lose on common evidence. E.g., Schleicher, 618 F.3d
at 685.
We appreciate the point, but the issue of causation in a
national market is also critical to plaintiffs’ case for class
certification. The fact that it also overlaps with their case on
the merits does not allow the district court to defer resolving
the factual issue.
IV. Expert Disputes Material to the Class Certification
A. The National Market Issue
We now come to the crux of the experts’ debates as they
affect class certification. Plaintiffs’ case on antitrust impact is
straightforward. Natural gas is a fungible commodity that is
transported relatively easily across the nation in a network of
pipelines. Dr. Harris and Dr. Dwyer studied the natural gas
market and vast quantities of data on transactions from the
class period. They concluded that the manipulated prices
tended to move together across the country, so that price

-- 17 of 30 --

18 No. 22-3279
manipulations by defendants in, say, Louisiana or Texas af-
fected the prices plaintiffs paid for natural gas in Wisconsin.
This theory for antitrust impact fits comfortably into eco-
nomic theory for this sort of commodity and with case law,
which treats horizontal price-fixing cases like this one as ap-
propriate for class action status.
The defendants argue that the antitrust impact/national
market issue is not as straightforward as plaintiffs contend.
The defense experts raise a host of issues with the methods
and conclusions of the plaintiffs’ experts. They point to the
variety of ways in which natural gas is sold and priced, in-
cluding spot prices, prices fixed for a month or for several
months, or prices indexed to various published prices. They
point to the differing lengths of time for which parties would
agree on pricing. And they point to what they contend are
anomalies in the data indicating that prices did not actually
move as predicted by plaintiffs’ experts’ model. They also
point to the role of brokers through whom many plaintiffs
purchased natural gas. Dkt. 213-1; 213-3; 213-4. These flaws,
the defendants argue, undermine the foundation for the Har-
ris Dwyer model, namely, a national market in natural gas.
Defendants also contend these flaws mean the case will re-
quire so much individualized evidence that the district court
should not have certified the class.
As noted, plaintiffs’ experts have responded to these criti-
cisms with detailed rebuttals. In the view of Dr. Harris and
Dr. Dwyer, the defense experts have distorted their work and
cherry-picked data to find a few anomalies that are easily ex-
plained within plaintiffs’ larger economic model. See Dkt.
225-6 & 225-9.

-- 18 of 30 --

No. 22-3279 19
We have reviewed these many detailed reports. In this ap-
peal, however, it is not our role to decide which experts have
the better of their debates with one another. For the reasons
explained above, the district court will need to engage with
these debates and make findings of fact, ultimately, as to
whether plaintiffs have shown the existence of a national mar-
ket in which defendants’ manipulations of prices affected the
prices plaintiff class members paid for the natural gas in Wis-
consin.
B. Guidance and Guardrails for Remand
As these issues have been framed for the district court and
for us, there is no shortcut that might let the district court
avoid full engagement with the economic experts and their
many and detailed point-counterpoint debates. That’s the
point of Comcast, along with West, Szabo, and Hydrogen Perox-
ide, among other cases. We can, however, offer some guide-
lines and guardrails for the proceedings on remand.
1. Manipulated Prices Sometimes Declined?
The defendants have argued that the evidence shows their
conduct occasionally diverged, “consistent with their traders’
divergent interests in raising or lowering prices at different
times based on their position in each transaction.” Dkt. 210 at
24. To the extent this evidence is aimed at refuting proof of
the alleged conspiracy, the existence of the conspiracy need
not be resolved at the class certification stage. To the extent
the evidence is aimed at undermining the existence of a na-
tional market, that is an issue that does need to be decided at
class certification.
Plaintiffs’ experts have responded that the evidence in
question came from activities of defendants’ trading arms,

-- 19 of 30 --

20 No. 22-3279
which were modest compared to the conspirators’ overall
market activity, and that the market manipulation had the
overall effect of driving prices dramatically higher during the
class period. We note that if defendants were in fact manipu-
lating the market prices to rise most of the relevant time, they
would not be entitled to credit for occasionally manipulating
the prices downward. E.g., Hawaii v. Standard Oil Co., 405 U.S.
251, 262 n.14 (1972) (where overcharge is proven, “courts will
not go beyond the fact of this injury to determine whether the
victim of the overcharge has partially recouped its loss in
some other way”); In re Nexium Antitrust Litig., 777 F.3d 9, 27
(1st Cir. 2015) (affirming class certification in face of similar
argument; collecting cases and saying “antitrust injury occurs
the moment the purchaser incurs an overcharge, whether or
not that injury is later offset”).
Moreover, the FERC Report noted that even if a certain
market participant were a net buyer of natural gas, unlawful
trading activity could increase the appearance of volatility,
raising prices and enabling a trader to work in agreement
with others to offload its unneeded gas at higher prices. FERC
Report at II-59. The MDL court in the District of Nevada ob-
served correctly that “a conspiracy can exist even though not
all members of the conspiracy participate in it in the exact
same way at the exact time and that some members of the con-
spiracy may in fact be at cross purposes at various times based
on their individual interests.” In re Western States, 2017 WL
1243135, at *2. Notwithstanding occasionally different inter-
ests, the plaintiffs contend, the defendants made many mil-
lions of dollars from their speculative trading arms.
Further, the plaintiffs have argued, ostensibly divergent
price activity would increase the price of fixed-price contracts.

-- 20 of 30 --

No. 22-3279 21
Dr. Dwyer explained: “The more variable daily prices are, the
more value there is in having a fixed price.…. To the extent
that market manipulations increased the variability of gas
prices, they would have increased” the price of fixed-price
contracts. Dkt. 208-13 at 20, ¶ 59; 21–22, ¶ 67.
2. Uniformity and Perfection Not Required
The plaintiffs’ theory is that the defendants’ conspiratorial
wash trades, churning, and false reporting caused the
plaintiffs to pay higher prices for natural gas in Wisconsin
because natural gas is a fungible commodity in a nationwide
market. In such a market, the plaintiffs explained, “prices
move up and down together across locations and purchasing
methods.” The defendants offered expert evidence showing,
they contend, that prices did not consistently move up and
down together; rather, depending on the location and price
type, prices of natural gas can go in opposite directions. The
defendants argue that “the existence of injury varied from
transaction to transaction within individual months and
among price types.” The defendants argue that the plaintiffs
cannot win certification unless they can show “a single
market that uniformly impacted all class members” or else
“unique circumstances” of each plaintiff’s purchase would
defeat predominance. Plaintiffs’ experts have offered
rebuttals to the examples cited by the defendants. More
fundamental, however, defendants overstate what is needed
to show that antitrust impact can be proven by evidence
common to all class members.
The defendants describe the various ways in which the
plaintiffs purchased gas. Even among fixed-price contracts
and index-price contracts, the plaintiffs’ purchasing methods
retain distinctions, including “trigger” contracts that would

-- 21 of 30 --

22 No. 22-3279
purchase gas if prices fell to a certain level “managed supply”
contracts, which would depend on managing supply for a
pool of customers, and various individualized hybrids. This
variety of arrangements means at least that price changes
would affect different class members at slightly different
times. To the extent that the plaintiffs purchased gas through
intermediaries, the defendants argue that the expert models
fail to reflect that the plaintiffs were paying for not only gas
but also other services. Consequently, the defendants argue,
these individual differences cause individual questions to
overwhelm common questions regarding causation of anti-
trust injury and the measurement of damages.
To the extent defendants are arguing this evidence defeats
the existence of a national market, we leave that question to
the plaintiffs’ experts’ rebuttals and ultimately to the district
court. But defendants also seem to argue that plaintiffs are re-
quired to prove that defendants’ antitrust violations affected
all class members to exactly the same degree at exactly the
same time. We rejected a similar challenge to class certifica-
tion in Messner v. Northshore University Health System. Plain-
tiffs there argued that defendants’ merger of hospital net-
works had raised prices for health care in hospitals. 669 F.3d
at 808. That case involved more extensive pricing problems
for complex packages or “baskets” of many different hospital
services, and there were similar complications from long-term
contracts, which could delay implementation of anticompeti-
tive pricing. Id. at 816. The district court had denied class cer-
tification on the ground that plaintiffs’ expert had not shown
uniform price increases for all class members. Id. at 817–18.
We reversed the denial of class certification, concluding
that the district court had demanded too much in terms of

-- 22 of 30 --

No. 22-3279 23
uniformity. Id. at 818. The key was that the plaintiffs’
economic expert had offered a common method for showing
impact on prices, even if it would produce different results for
different individual class members in calculating damages. Id.
at 818–19; see also Bogosian v. Gulf Oil Corp., 561 F.2d 434, 455
(3d Cir. 1977) (“If the price structure in industry is such that
nationwide the conspiratorially affected prices at the
wholesale level … though different in different regions,
[were] higher … than the range which would have existed …
under competitive conditions, it would be clear that all
members of the class suffered some damage, notwithstanding
that there would be variations among all dealers as to the
extent of their damage.”), abrogation on other grounds
recognized in In re Insurance Brokerage Antitrust Litig., 618 F.3d
300, 325 n.25 (3d Cir. 2010); In re Urethane Antitrust Litig., 768
F.3d 1245, 1255 (10th Cir. 2014) (affirming jury verdict for
plaintiff class; “district judge could reasonably weigh the
evidence and conclude that price-fixing would have affected
the entire market, raising the baseline prices for all buyers.
Based on the reasonableness of this finding, the judge had the
discretion to treat impact as a common question that was
capable of class-wide proof”).
As we noted in Messner, real-world markets “are not as
simple and elegant as the classic economic model….” 669 F.3d
at 816. The vast amounts of natural gas pricing data reflect
that complexity, and sound economic findings are not neces-
sarily elegant. That points us to another important guideline
on remand, well established in our antitrust law: perfect proof
is not required. It sometimes can be tempting for courts to
look so hard for perfect evidence that the search becomes the
enemy of quite good evidence. That can be a mistake.

-- 23 of 30 --

24 No. 22-3279
If the plaintiffs can show that the common method
accounts for differences in methods of purchasing and pricing
natural gas cited by defendants, it will be permissible to infer
impact and to “make a reasonable estimation of actual
damages through probability and inference.” Loeb Industries,
Inc. v. Sumitomo Corp., 306 F.3d 469, 490 (7th Cir. 2002). “In
essence, it is important not to let a quest for perfect evidence
become the enemy of good evidence.” Messner, 669 F.3d at
808.
The Supreme Court made the same point in Comcast: “Cal-
culations need not be exact.” 569 U.S. at 35. In support, the
Court cited Story Parchment Co. v. Paterson Parchment Paper Co.,
which also supports the principle:
Where the tort itself is of such a nature as to
preclude the ascertainment of the amount of
damages with certainty, it would be a
perversion of fundamental principles of justice
to deny all relief to the injured person, and
thereby relieve the wrongdoer from making any
amend for his acts. In such case, while the
damages may not be determined by mere
speculation or guess, it will be enough if the
evidence show the extent of the damages as a
matter of just and reasonable inference,
although the result be only approximate. The
wrongdoer is not entitled to complain that they
cannot be measured with the exactness and
precision that would be possible if the case,
which he alone is responsible for making, were
otherwise.
282 U.S. 555, 563 (1931).

-- 24 of 30 --

No. 22-3279 25
3. Not Every Class Member and Not Every Transaction
Two closely related points are that class certification does
not require proof that every class member was injured or that
every gas purchase was affected by the conspiracy. To the
extent the defendants suggest that before class certification,
the plaintiffs must show all class members suffered some
injury, that is not correct. We have said this repeatedly. E.g.,
Kleen Products LLC v. International Paper Co., 831 F.3d 919, 927
(7th Cir. 2016); Suchanek v. Sturm Foods, Inc., 764 F.3d 750, 757
(7th Cir. 2014) (“If the court thought that no class can be
certified until proof exists that every member has been
harmed, it was wrong.”); Parko, 739 F.3d at 1084–85;
McReynolds v. Merrill Lynch, Pierce, Fenner & Smith, Inc., 672
F.3d 482, 490–91 (7th Cir. 2012). We explained in Kohen v.
Pacific Investment Management Co. LLC, 571 F.3d 672, 677 (7th
Cir. 2009), that “a class should not be certified if it is apparent
that a great many persons who have suffered no injury at the
hands of the defendant….” We have also explained that,
“[t]here is no precise measure for ‘a great many.’ Such
determinations are a matter of degree, and will turn on the
facts as they appear from case to case.” Messner, 669 F.3d at
825; see also Olean Wholesale Grocery Cooperative, Inc. v. Bumble
Bee Foods LLC, 31 F.4th 651, 669 (9th Cir. 2022) (rejecting rule
precluding class certification when class might include more
than “de minimis” number of uninjured members). Also, if
the class definition truly were too broad or heterogenous, the
class definition could be adjusted or subdivided. Kohen, 571
F.3d at 680; see also Fed. R. Civ. P. 23(c)(5).
Plaintiffs also do not need to prove that every gas purchase
by a class member during the class period was affected by the
conspiracy. A class member has a claim if any purchase

-- 25 of 30 --

26 No. 22-3279
during the class period was affected by the conspiracy. For
example, some named plaintiffs entered into fixed-price con-
tracts before the class period began that lasted well into the
class period. The prices they paid early in the class period un-
der those contracts should not have been affected by any con-
spiratorial price manipulation. But those plaintiffs all appear
to have entered into later contracts that took effect during the
class period, when, according to plaintiffs’ experts, the prices
they paid had been raised by the conspiracy’s manipulations.
4. Actions of Non-defendant Co-conspirators
Defendants also criticize plaintiffs’ experts for their
reliance upon data showing sales and sales reports by non-
defendants. It’s not clear how this criticism affects class
certification, at least if plaintiffs can prove the existence of a
national market. The extent of the conspiracy will be a matter
for proof at trial, by evidence common to all class members.
The actions of non-defendant co-conspirators will be fair
game at trial. “[E]ach member of a conspiracy is liable for all
damages caused by the conspiracy’s entire output.” Paper
Systems Inc. v. Nippon Paper Industries Co., 281 F.3d 629, 632
(7th Cir. 2002), citing Texas Industries, Inc. v. Radcliff Materials,
Inc., 451 U.S. 630 (1981). Not all co-conspirators need to be
named defendants. See id. And a “co-conspirator who joins a
conspiracy with knowledge of what has gone on before and
with an intent to pursue the same objectives may, in the
antitrust context, be charged with the preceding acts of its co-
conspirators.” Kleen, 831 F.3d at 930 (internal quotation marks
omitted), quoting Havoco of America, Ltd. v. Shell Oil Co., 626
F.2d 549, 554 (7th Cir. 1980). The defendants’ argument about
non-defendants’ false reporting thus reduces to the merits of
the conspiracy allegation itself. The existence of the

-- 26 of 30 --

No. 22-3279 27
conspiracy and whether non-defendant companies’
transactions were part of it are, as earlier described, common
to the class. If the plaintiffs cannot show the non-defendant
transactions were part of the conspiracy of the defendants,
then that goes to the magnitude of impact and amount of
damages, not predominance.
5. Full-Consideration Claim
As noted above, Wisconsin law provides an unusual anti-
trust remedy: “full consideration.” See Wis. Stat. § 133.14. The
statute makes void all contracts that are a product of antitrust
conspiracy: “All contracts or agreements made by any person
while a member of any conspiracy prohibited by § 133.03, and
which contract or agreement is founded upon, is the result of,
or grows out of or is connected with any violation of such sec-
tion, either directly or indirectly, shall be void ….” Id. Parties
who have made payments under such contracts are entitled
to full refunds: “Any payment made upon, under or pursuant
to such contract or agreement to or for the benefit of any per-
son may be recovered from any person who received or ben-
efited from such payment .…” Id.
On remand the district court may find it helpful to con-
sider this remedy separately from the treble-damages remedy
more familiar from federal antitrust law. For purposes of class
certification, calculating damages should be much simpler for
the “full consideration” remedy. The statutory language calls
for a causal connection between the contract and the conspir-
acy, but it is phrased quite broadly: “is founded upon, is the
result of, or grows out of or is connected with any violation
….” Id.

-- 27 of 30 --

28 No. 22-3279
V. Class Certification Available on This Record
One last issue: We have explained why we must vacate the
certification of the class and remand for further consideration
and fact-finding on the disputed issues affecting antitrust im-
pact and thus predominance of common issues. In their briefs
on appeal, however, defendants reach further. They argue
that the district court could not properly certify a plaintiff class
on this record. Defendants would have us order the district
court simply to deny class certification. We reject that pro-
posal.
Defendants seek support from Comcast Corp. v. Behrend,
569 U.S. 27 (2013), but a close look at that case shows critical
differences. Most important, Comcast did not involve price-
fixing, which makes the question of antitrust impact much
simpler here than in Comcast. At its core, Comcast was a mo-
nopolization case involving business tactics for which anti-
trust impact was less well-recognized than it is for horizontal
price-fixing alleged here. Plaintiffs in Comcast challenged a
strategy called “clustering,” through which Comcast alleg-
edly made “swap” deals with other cable television providers
to let each build up large market shares in particular metro-
politan or regional markets. Id. at 29–30. The plaintiff consum-
ers offered four theories of antitrust impact from these
“swaps” and concentrations of market power. Id. at 31. The
district court had accepted only one of those theories and re-
jected the other three. The problem for class certification was
that the plaintiffs’ theory for a common method of proving
damages assumed the validity of all four theories of antitrust
impact. As a result, the plaintiffs’ damages theory was no
longer consistent with their liability theory. Id. at 35.

-- 28 of 30 --

No. 22-3279 29
This case is fundamentally different. Horizontal price-
fixing is the most basic, core antitrust violation. Bork, The
Antitrust Paradox, supra, at 67. Its empirical effects—prices
higher than would prevail in a competitive market—are the
archetype, the paradigm, the Platonic form of antitrust
impact. An empirical model that reliably estimates the effects
of the price-fixing satisfies the needs of class certification.
Defendants point out that plaintiffs here allege the con-
spirators used different methods for fixing prices: “churning,”
wash sales, and fraudulent reports. Defendants then try to
equate those different methods with the Comcast plaintiffs’
different theories of antitrust impact. The argument tries to
compare apples to oranges. The conspirators’ different mech-
anisms to manipulate natural gas prices are all illegal. There
is no need for plaintiffs and their experts here to try to distin-
guish among those methods and any supposedly different ef-
fects, or to distinguish among the conspirators depending on
who used which methods, when, and where. Comcast calls for
the district court to engage with the merits of the experts’ de-
bate over causation and antitrust impact, but it does not show
that certification would be inappropriate here.
On the core issues—the nuts and bolts of the disputes over
what the economic data show about the effects of price ma-
nipulation in the natural gas market—plaintiffs’ experts have
offered detailed rebuttals to the defense experts’ selections of
data and arguments. We would not be surprised if a class can
be properly certified here after sufficient “rigorous analysis”
of the experts’ debates. After all, the case presents a conspir-
acy to manipulate prices for a fungible commodity traded
across a nationwide network of pipelines.

-- 29 of 30 --

30 No. 22-3279
* * *
We know that we are demanding a great deal from the
district court on remand. The expert testimony relevant to the
Wisconsin antitrust impact issue is laid out in around a dozen
reports, not to mention the tables, charts, and deposition
testimony. The parties’ experts have been debating each other
in this litigation since at least 2009, and the key reports were
all filed in class certification debates in Nevada and then
refiled several years later in Wisconsin. Complicating this case
still further, the four experts debating the Wisconsin antitrust
impact issue were parts of larger teams of experts addressing
a host of other issues. The relevant reports also contain a good
deal of information on other issues and other states. On
remand here, it will be necessary for the district court to dig
into these debates among the experts. Given the number of
reports and issues, the district court will be entitled to expect
from counsel a guided tour of the expert evidence, perhaps
with a guide comparable to detailed flow-charts familiar to
competitive debaters. It might make sense for counsel for both
parties to collaborate on making such a chart, and the court
can determine what would be most helpful.
The order certifying the plaintiff class is VACATED and
the case is REMANDED to the district court for further
consideration of class certification consistent with this
opinion.

-- 30 of 30 --