                   FOR PUBLICATION
  UNITED STATES COURT OF APPEALS
       FOR THE NINTH CIRCUIT

UNITED STEEL, PAPER & FORESTRY,          
RUBBER, MANUFACTURING ENERGY,
ALLIED INDUSTRIAL & SERVICE
WORKERS INTERNATIONAL UNION,
AFL-CIO, CLC, On behalf of its
members employed by defendants;
RAUDEL COVARRUBIAS, individually
and on behalf of all similarly
situated current and former                     No. 09-56578
employees; DAVID SIMMONS,
individually and on behalf of all                 D.C. No.
                                             2:08-cv-02068-PSG-
similarly situated current and
                                                     FFM
former employees; STEPHEN S.
SWADER Sr., individually and on
behalf of all similarly situated
current and former employees,
                Plaintiffs-Appellants,
                  v.
CONOCOPHILLIPS COMPANY,
                Defendant-Appellee.
                                         




                              377
378             UNITED STEEL v. CONOCOPHILLIPS



UNITED STEEL, PAPER & FORESTRY,          
RUBBER, MANUFACTURING ENERGY,
ALLIED INDUSTRIAL & SERVICE
WORKERS INTERNATIONAL UNION,
AFL-CIO, CLC, On behalf of its
members employed by defendants;
RAUDEL COVARRUBIAS, individually
and on behalf of all similarly
                                                No. 09-56579
situated current and former
employees; DAVID SIMMONS,                          D.C. No.
individually and on behalf of all           2:08-cv-02068-PSG-
similarly situated current and                       FFM
former employees; STEPHEN S.                      OPINION
SWADER Sr., individually and on
behalf of all similarly situated
current and former employees,
                 Plaintiffs-Appellees,
                  v.
CONOCOPHILLIPS COMPANY,
               Defendant-Appellant.
                                         
        Appeal from the United States District Court
            for the Central District of California
        Philip S. Gutierrez, District Judge, Presiding

                 Argued and Submitted
          November 4, 2009—Pasadena, California

                     Filed January 6, 2010

        Before: Thomas G. Nelson, Jay S. Bybee, and
             Milan D. Smith, Jr., Circuit Judges.

                   Opinion by Judge Bybee
                UNITED STEEL v. CONOCOPHILLIPS              381
                          COUNSEL

Anne Richardson, Hadsell, Stormer, Keeny, Richardson &
Renick, LLP, Pasadena, California, for plaintiffs-appellants-
appellees Raudel Covarrubias, David Simmons, and Stephen
S. Swader, Sr.

Robert A. Cantore, Gilbert & Sackman, Inc., Los Angeles,
California, for plaintiff-appellant-appellee United Steel, Paper
& Forestry, Rubber, Manufacturing, Energy, Allied Industrial
& Service Workers International Union, AFL-CIO, CLC.

Rex S. Heinke, Akin Gump Strauss Hauer & Feld, LLP, Los
Angeles, California, for defendant-appellant-appellee Cono-
coPhillips Co.


                          OPINION

BYBEE, Circuit Judge:

   These consolidated appeals raise two issues: first, whether
the district court abused its discretion when it denied plain-
tiffs’ motion to certify a putative class out of concern that
practical obstacles could potentially develop if plaintiffs’
legal theory were ultimately rejected; and second, whether the
district court erred in remanding, in light of its certification
decision, state law claims to state court for lack of subject
matter jurisdiction. We hold that the district court abused its
discretion when it assumed, for the purpose of Federal Rule
of Civil Procedure 23 certification analysis and without any
separate inquiry into the merits, that plaintiffs’ legal theory
would fail. Accordingly, we reverse and remand for reconsid-
eration of plaintiffs’ certification motion and dismiss as moot
the appeal of the remand order.
382                UNITED STEEL v. CONOCOPHILLIPS
                                     I

   Defendant ConocoPhillips Company is an international oil
company that operates oil refineries in Los Angeles,1 Santa
Maria, and Rodeo, California. United Steel, Paper & Forestry,
Rubber, Manufacturing, Energy, Allied Industrial & Service
Workers International Union, AFL-CIO, CLC (“USW”) is a
labor union that represents many of the employees who work
at ConocoPhillips’ refineries. ConocoPhillips and USW are
parties to a collective bargaining agreement that sets forth
wages, hours, and working conditions for USW-represented
employees at ConocoPhillips’ California refineries.

   On February 15, 2008, USW and representative plaintiffs
David Simmons, Raudel Covarrubias, and Stephen Swader2
filed a class action complaint against ConocoPhillips and ten
John Doe Defendants in Los Angeles Superior Court. The
complaint sought “class-wide relief under California law for
defendants’ breaches of their legal obligation to provide
employees with unpaid, 30-minute meal periods, totally
relieved of all duties, for every 5 hours of work.” The basic
premise of plaintiffs’ complaint was that because operators
cannot leave their units during their meal breaks and are sub-
ject to interruptions to which they must respond, their meal
periods are “on duty” within the meaning of California law.3
Plaintiffs sought both damages and injunctive relief.
  1
     ConocoPhillips’ Los Angeles refinery is composed of two linked facili-
ties located approximately five miles apart in Carson and Wilmington.
   2
     The representative plaintiffs are various types of operators at the Los
Angeles and Santa Maria ConocoPhillips refineries. No representative
plaintiff is a laboratory employee, nor does any representative plaintiff
work at the Rodeo refinery.
   3
     In order for an “on duty” meal period to be permissible under Califor-
nia law, all three of the following conditions must be met: (1) the nature
of the work must prevent the employee from being relieved of all duty
during the meal period; (2) the employee and employer must have entered
into a written agreement authorizing an on duty meal period; and (3) the
                    UNITED STEEL v. CONOCOPHILLIPS                        383
   On March 27, 2008, ConocoPhillips removed the action to
the United States District Court for the Central District of Cal-
ifornia, citing the Class Action Fairness Act of 2005
(“CAFA”), Pub. L. No. 109-2, 119 Stat. 4 (codified at 28
U.S.C. §§ 1332(d), 1453, 1711-15), as the basis for federal
subject matter jurisdiction. CAFA vests a district court with
original jurisdiction over “a class action” where: (1) there are
one-hundred or more putative class members; (2) at least one
class member is a citizen of a state different from the state of
any defendant; and (3) the aggregated amount in controversy
exceeds $5 million, exclusive of costs and interest. 28 U.S.C.
§§ 1332(d)(2), (5)(B), (6). In its notice of removal, Cono-
coPhillips stated that “Plaintiffs, at the time this action was
commenced, were citizens and residents of the State of Cali-
fornia,” while ConocoPhillips, as a Delaware corporation with
its principal place of business in Texas, was not a citizen of
California under 28 U.S.C. § 1332(c)(1). Plaintiffs did not
contest removal.

   After removal, the parties proceeded with discovery, and in
early 2009, plaintiffs moved for class certification under Fed-
eral Rule of Civil Procedure 23. The putative class encom-
passed

     all former, current, and future non-exempt hourly
     employees of Defendant ConocoPhillips who, at any
     time since February 15, 2004, worked as an Operator

written agreement must expressly state that the employee may, in writing,
revoke the agreement at any time. Cal. Code Regs. tit. 8, § 11010, subd.
11(C); see also DLSE Opinion Letter 2002-09-04.
   The specifics of the labor dispute underlying plaintiffs’ suit are not rele-
vant to the certification question at issue in this appeal. However, the gra-
vamen of plaintiffs’ complaint is that because operators at
ConocoPhillips’s California refineries must respond to their radios and to
any audible alarms throughout their twelve-hour shifts, any meal breaks
operators take are “on duty” under California law and must be compen-
sated as such.
384                UNITED STEEL v. CONOCOPHILLIPS
      or in the laboratory on a shift schedule at a Cono-
      coPhillips refinery located in Los Angeles, Santa
      Maria, or Rodeo, California.

   On March 16, 2009, the district court denied class certifica-
tion, but did so without prejudice. In this order, the district
court held that although plaintiffs had demonstrated the exis-
tence of three of the four Rule 23(a) prerequisites to class cer-
tification — numerosity, commonality, and typicality, see
Fed. R. Civ. P. 23(a)(1)-(3) — plaintiffs failed to satisfy the
“adequate representation” requirement under Rule 23(a)(4).
Specifically, the district court held that due to counterclaims
then pending against USW, “USW’s interests [we]re not
properly aligned with those of the class” and that because
then-class counsel also represented USW, “it could not ade-
quately represent the interests of the class.”

   After the March 2009 order, the representative plaintiffs
obtained new counsel unrelated to USW, USW successfully
moved for Rule 12(b)(6) dismissal of all pending counter-
claims against it, and plaintiffs renewed their motion for class
certification under Rule 23. In an order dated June 11, 2009,
the district court again denied class certification. The district
court held that plaintiffs had satisfied all four requirements of
Rule 23(a), but failed to satisfy any of the three provisions in
Rule 23(b).4 The court held that although plaintiffs had relied
on both Rule 23(b)(2) and Rule 23(b)(3) in support of class
certification, plaintiffs had not carried their burden of satisfy-
ing either of these provisions. With respect to Rule 23(b)(3),
the so-called “predominance” requirement, the district court
reasoned that “if Plaintiffs’ ‘on duty’ theory is rejected . . . the
Court will be faced with a case . . . requiring individualized
trials on each class member’s meal period claims,” and “a
  4
   Although a putative class must satisfy all four requirements of Rule
23(a) to achieve certification, the three provisions of Rule 23(b) are dis-
junctive: a class can be certified where it satisfies only one Rule 23(b)
requirement.
                   UNITED STEEL v. CONOCOPHILLIPS                      385
class action w[ould] not be the superior method of resolving
this suit.” The court ultimately held that “this problem . . . is
an insurmountable barrier to class certification,” and therefore
“decline[d] to certify the class under Rule 23(b)(3).”

   The same day it issued the order denying certification, the
district court remanded this action to Los Angeles Superior
Court. The district court explained that “district courts are
split on the issue” of whether remand is required after denial
of class certification and noted that “[t]he Ninth Circuit has
never addressed this question,” before ultimately concluding:

      In the instant case there is no “reasonably foresee-
      able possibility” that a class will be certified, given
      that Plaintiffs have brought two unsuccessful certifi-
      cation motions and that insurmountable problems
      preclude certification under Rule 23(b)(3). The
      Court is persuaded by the reasoning of these authori-
      ties: a determination that class certification is not a
      “reasonably foreseeable possibility” is not a post-
      removal change in jurisdictional facts, but rather is
      equivalent to a finding that jurisdiction never existed
      under CAFA in the first place. Accordingly, CAFA
      does not provide a basis for jurisdiction over this
      action.

(Internal citations omitted).

   Having held that CAFA did not provide subject matter
jurisdiction, the district court then rejected any other possible
bases for jurisdiction, including supplemental jurisdiction and
diversity jurisdiction. Finding no subject matter jurisdiction
over this case, the district court remanded to Los Angeles
Superior Court.5
  5
   After the district court remanded, plaintiffs’ Case Management State-
ments in state court continued to assert that this case was a class action,
indicated that class certification would be sought, and sought class discov-
386                UNITED STEEL v. CONOCOPHILLIPS
   Plaintiffs timely petitioned for permission to appeal the
June 2009 order denying class certification, and ConocoPhil-
lips timely petitioned for permission to appeal the remand
order. On September 30, 2009, this court granted both parties’
petitions to appeal. We reverse and remand in plaintiffs’
appeal of the order denying certification and dismiss as moot
ConocoPhillips’ appeal of the order remanding this case to
state court.6

                                     II

   [1] Federal Rule of Civil Procedure 23, which governs class
certification, contains two distinct sets of requirements. Rule
23(a) outlines four requirements, all of which must be met for
class certification: (1) the class must be so numerous that join-
der of all members is impracticable; (2) there must be ques-
tions of law or fact common to the class; (3) the claims or
defenses of the class representatives must be typical of the
claims or defenses of the class; and (4) the class representa-

ery. In response to plaintiffs’ filings, ConocoPhillips again removed to dis-
trict court under CAFA. Plaintiffs filed a motion for remand, asserting that
because the district court had held that class certification was not reason-
ably possible, there could be no CAFA jurisdiction. The district court ulti-
mately granted plaintiffs’ remand motion, holding that ConocoPhillips
failed to present new facts or events sufficient to justify its second removal
attempt.
   6
     CAFA imposes strict deadlines for the rendering of judgment by
Courts of Appeals. Under 28 U.S.C. § 1453(c)(2), “[i]f the court of
appeals accepts an appeal under paragraph (1), the court shall complete all
action on such appeal, including rendering judgment, not later than 60
days after the date on which such appeal was filed, unless an extension is
granted under paragraph (3)” (emphasis added). Paragraph (3) provides
that “[t]he court of appeals may grant an extension of the 60-day period
described in paragraph (2) if — (A) all parties to the proceeding agree to
such extension, for any period of time; or (B) such extension is for good
cause shown and in the interests of justice, for a period not to exceed 10
days.” Id. § 1453(c)(3). Both parties graciously agreed to an extension in
this case, and we grant an extension to the filing of this opinion.
                UNITED STEEL v. CONOCOPHILLIPS                387
tives must fairly and adequately protect the interests of all
members of the class. Fed. R. Civ. P. 23(a). The four require-
ments of Rule 23(a) are commonly referred to as “numerosi-
ty,” “commonality,” “typicality,” and “adequacy of
representation” (or just “adequacy”), respectively. See, e.g.,
Rodriguez v. Hayes, 578 F.3d 1032, 1047-51 (9th Cir. 2009).
Where a putative class satisfies all four requirements of Rule
23(a), it still must meet at least one of three additional
requirements outlined in Rule 23(b) in order to be eligible for
certification. Rule 23(b) provides that

    [a] class action may be maintained if Rule 23(a) is
    satisfied and if:

    (1) prosecuting separate actions by or against indi-
    vidual class members would create a risk of:

       (A) inconsistent or varying adjudications with
    respect to individual class members that would
    establish incompatible standards of conduct for the
    party opposing the class; or

       (B) adjudications with respect to individual class
    members that, as a practical matter, would be dispo-
    sitive of the interests of the other members not par-
    ties to the individual adjudications or would
    substantially impair or impede their ability to protect
    their interests;

    (2) the party opposing the class has acted or refused
    to act on grounds that apply generally to the class, so
    that final injunctive relief or corresponding declara-
    tory relief is appropriate respecting the class as a
    whole; or

    (3) the court finds that the questions of law or fact
    common to class members predominate over any
    questions affecting only individual members, and
388                UNITED STEEL v. CONOCOPHILLIPS
      that a class action is superior to other available meth-
      ods for fairly and efficiently adjudicating the contro-
      versy. The matters pertinent to these findings
      include:

        (A) the class members’ interests in individually
      controlling the prosecution or defense of separate
      actions;

        (B) the extent and nature of any litigation concern-
      ing the controversy already begun by or against class
      members;

         (C) the desirability or undesirability of concentrat-
      ing the litigation of the claims in the particular
      forum; and

        (D) the likely difficulties in managing a class
      action.

Fed. R. Civ. P. 23(b). The requirement outlined in Rule
23(b)(3) is generally referred to as “predominance” and is the
focus of plaintiffs’ appeal.7

  The party seeking class certification bears the burden of
demonstrating that the requirements of Rules 23(a) and (b) are
met. See Zinser v. Accufix Research Inst., Inc., 253 F.3d 1180,
1186 (9th Cir. 2001). Rule 23(b) states:

      A class action may be maintained if Rule 23(a) is
      satisfied and if . . . (3) the court finds that the ques-
      tions of law or fact common to class members pre-
  7
    The district court held that although plaintiffs had satisfied all four
Rule 23(a) requirements, they did not establish an entitlement to certifica-
tion under Rule 23(b)(2) or (3). Plaintiffs did not argue that they had satis-
fied Rule 23(b)(1). On this appeal, plaintiffs have disavowed any reliance
on Rule 23(b)(2) and argue only that the district court erred in holding that
plaintiffs did not satisfy Rule 23(b)(3).
                 UNITED STEEL v. CONOCOPHILLIPS                  389
     dominate over any questions affecting only
     individual members, and that a class action is supe-
     rior to other available methods for fairly and effi-
     ciently adjudicating the controversy. . . .

   We review both the ultimate decision whether to certify a
class and the underlying determination whether the predomi-
nance requirement of Rule 23(b)(3) has been satisfied for
abuse of discretion. See Zinser, 253 F.3d at 1186 (class certi-
fication generally), 1192 (predominance).

  In holding that Rule 23(b)(3) posed an “insurmountable
barrier to class certification” in this case, the district court rea-
soned:

     Defendant correctly points out that if Plaintiffs’ “on
     duty” theory of liability fails, then common ques-
     tions will no longer predominate over individual
     ones. In other words, if it is ultimately determined
     that (1) class members’ meal periods were not “on
     duty” or, alternatively, that (2) the conditions prereq-
     uisite to a lawful “on duty” meal period were satis-
     fied, then in order to establish Defendant’s liability,
     Plaintiffs will need to show that they actually missed
     meal breaks.

The district court then stated that it appeared that “the exis-
tence of a uniform policy as to the availability of a meal
period could be proved on a classwide basis . . . .” However,
in the district court’s view, “there c[ould] be no assurances
that [plaintiffs] w[ould] prevail on [their ‘on duty’] theory.”
And if plaintiffs did not prevail on this theory, the district
court reasoned, the inquiry would then shift to whether plain-
tiffs actually missed meal breaks, and “the Court w[ould] be
faced with a case . . . requiring individualized trials on each
class member’s meal period claims,” thus making “a class
action . . . not . . . the superior method of resolving this suit.”
390             UNITED STEEL v. CONOCOPHILLIPS
   As support for its conclusion that the possibility of numer-
ous future mini-trials proved “an insurmountable barrier to
class certification” under Rule 23(b)(3), the district court
quoted an Eleventh Circuit decision, Andrews v. American
Telephone & Telegraph Co., 95 F.3d 1014, 1023 (11th Cir.
1996), which in turn quoted a decision by the Fourth Circuit,
Windham v. American Brands, Inc., 565 F.2d 59, 70 (4th Cir.
1977), stating: “[A] district court should not decline to certify
a class because it fears that insurmountable problems may
later appear. But where the court finds, on the basis of sub-
stantial evidence as here, that there are serious problems now
appearing, it should not certify the class merely on the assur-
ance of counsel that some solution will be found.” (alteration
in district court order).

   “We limit our [certification] review to whether the district
court correctly selected and applied Rule 23’s criteria. An
abuse of discretion occurs when the district court, in making
a discretionary ruling, relies upon an improper factor, omits
consideration of a factor entitled to substantial weight, or
mulls the correct mix of factors but makes a clear error of
judgment in assaying them.” Parra v. Bashas’, Inc., 536 F.3d
975, 977-78 (9th Cir. 2008) (internal quotation marks and
citation omitted). Plaintiffs’ basic argument is that the district
court abused its discretion by declining certification based on
the possibility that plaintiffs would not prevail on the merits
on their “on duty” theory. We agree.

  [2] Critically, the district court did not hold that plaintiffs’
actual legal theory (what the district court referred to as
“Plaintiffs’ ‘on duty’ theory of liability”) was one in which
common issues of law or fact did not predominate over indi-
vidual questions. Instead, the district court treated plaintiffs’
actual legal theory as all but beside the point, holding that
because “there can be no assurances that [plaintiffs] w[ould]
prevail on this theory,” (emphasis added), the district court’s
predominance inquiry would instead focus on the question
whether plaintiffs “actually missed meal breaks,” an admit-
                UNITED STEEL v. CONOCOPHILLIPS                391
tedly individualized inquiry. By refusing to analyze plaintiffs’
“on duty” argument as the basis for its predominance inquiry
because “there c[ould] be no assurances that they w[ould]
prevail on this theory,” the district court ignored Ninth Circuit
precedent and ultimately abused its discretion.

   [3] “In determining the propriety of a class action, the ques-
tion is not whether the plaintiff or plaintiffs have stated a
cause of action or will prevail on the merits, but rather
whether the requirements of Rule 23 are met[,]” and “nothing
in either the language or history of Rule 23 . . . gives a court
any authority 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, 177-78 (1974) (quotation marks and citation omitted).
Although certification inquiries such as commonality, typical-
ity, and predominance might properly call for some substan-
tive inquiry, “[t]he court may not go so far . . . as to judge the
validity of these claims.” Staton v. Boeing Co., 327 F.3d 938,
954 (9th Cir. 2003). “[N]either the possibility that a plaintiff
will be unable to prove his allegations, nor the possibility that
the later course of the suit might unforeseeably prove the orig-
inal decision to certify the class wrong, is a basis for declining
to certify a class which apparently satisfies [Rule 23].” Blac-
kie v. Barrack, 524 F.2d 891, 901 (9th Cir. 1975).

   [4] Here, the district court not only “judge[d] the validity”
of plaintiffs’ “on duty” claims, it did so using a nearly insur-
mountable standard, concluding that merely because it was
not assured that plaintiffs would prevail on their primary legal
theory, that theory was not the appropriate basis for the pre-
dominance inquiry. But a court can never be assured that a
plaintiff will prevail on a given legal theory prior to a disposi-
tive ruling on the merits, and a full inquiry into the merits of
a putative class’s legal claims is precisely what both the
Supreme Court and we have cautioned is not appropriate for
a Rule 23 certification inquiry. See Eisen, 417 U.S. at 177-78;
Cummings v. Connell, 316 F.3d 886, 896 (9th Cir. 2003) (not-
392              UNITED STEEL v. CONOCOPHILLIPS
ing that “this circuit does not favor denial of class certification
on the basis of speculative conflicts”); Staton, 327 F.3d at
954; Moore v. Hughes Helicopters, Inc., 708 F.2d 475, 480
(9th Cir. 1983) (holding that “it is improper to advance a deci-
sion on the merits to the class certification stage”).

    The only legal authority cited by the district court for its
decision to ignore plaintiffs’ “on duty” legal theory in its pre-
dominance analysis was the Eleventh Circuit’s decision in
Andrews v. American Telephone & Telegraph Co., 95 F.3d
1014. We do not think Andrews bears the weight assigned it
by the district court. In Andrews, a district court in Georgia
certified two classes totaling several million members in liti-
gation raising legal claims premised on the gaming laws of all
fifty states and involving telephone calls to “hundreds of
widely differing 900-number programs.” Id. at 1023. The
Eleventh Circuit held that the district court abused its discre-
tion in certifying these classes due to the fact that the district
court would have to “try millions of small claims,” id., citing
a Fourth Circuit case from 1977 for the proposition that
“while the district court should not decline to certify a class
because it fears that insurmountable problems may later
appear, if the court finds that there are serious problems now
appearing, it should not certify the class merely on the assur-
ance that some solution will be found.” Id. (internal quotation
marks, ellipses, and citation omitted). Andrews is simply
nothing like this case: in Andrews, the plaintiffs’ own legal
theory required millions of mini-trials, a clear case of “serious
problems now appearing,” while in this case the prospect of
mini-trials would only appear if plaintiffs’ legal theory were
actually rejected on its merits, a clear case of a “problem[
that] may later appear.”

   [5] Moreover, a district court retains the flexibility to
address problems with a certified class as they arise, including
the ability to decertify. “Even after a certification order is
entered, the judge remains free to modify it in the light of sub-
sequent developments in the litigation.” Gen. Tel. Co. of the
                UNITED STEEL v. CONOCOPHILLIPS               393
Sw. v. Falcon, 457 U.S. 147, 160 (1982); see also Rodriguez
v. West Publ’g Corp., 563 F.3d 948, 966 (9th Cir. 2009) (“A
district court may decertify a class at any time.”); Cummings,
316 F.3d at 896 (finding “the district court’s approach [to be]
entirely appropriate” where the court determined that a poten-
tial class “conflict was too speculative at the time [of the cer-
tification motion] to prevent finding the named plaintiffs to be
adequate representatives,” but “remained willing to reconsider
and decertify the class if . . . there was evidence of an actual
conflict”); Armstrong v. Davis, 275 F.3d 849, 871 n.28 (9th
Cir. 2001) (“Federal Rule of Civil Procedure 23 provides dis-
trict courts with broad discretion to determine whether a class
should be certified, and to revisit that certification throughout
the legal proceedings before the court.”). What a district court
may not do is to assume, arguendo, that problems will arise,
and decline to certify the class on the basis of a mere potenti-
ality that may or may not be realized. If, on remand, the dis-
trict court certifies the class and plaintiffs’ “on duty” legal
theory is ultimately rejected, the district court can revisit its
certification decision at that time. See Cummings, 316 F.3d at
896.

                               III

   [6] We remand to the district court for reconsideration of
plaintiffs’ motion for class certification in light of our deci-
sion. With respect to the proceedings on remand, we note that
“[w]hile the court may not put the plaintiff[s] to preliminary
proof of [their] claim[s], it does require sufficient information
to form a reasonable judgment,” and “may request the parties
to supplement the pleadings with sufficient material to allow
an informed judgment on each of the Rule[ 23] requirements.”
Blackie, 524 F.2d at 901 n.17.

   Because we find the district court abused its discretion in
its order denying certification, we need not address the issue
raised by ConocoPhillips’ appeal.
394           UNITED STEEL v. CONOCOPHILLIPS
   The judgment in No. 09-56578 is REVERSED; the appeal
in No. 09-56579 is DISMISSED AS MOOT. The parties shall
bear their own costs on appeal.
