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                                                        Exhibit 10.12(b)

                   AMENDMENT TO THE CCC/WPC SERVICES AGREEMENT

          This Amendment to the CCC/WPC Services Agreement between Chevron
Chemical Company and Warren Petroleum Company, Limited Partnership, dated as
of the 1st day of September, 1996 (the "Services Agreement"), is made and
entered into by CHEVRON CHEMICAL COMPANY, LLC, a Delaware limited liability
company ("CCCLLC"), and WARREN PETROLEUM COMPANY, LIMITED PARTNERSHIP, a
Delaware limited partnership ("Warren"), as of this 18th day of May, 1998.

                                 R E C I T A L S

          WHEREAS, CCCLLC is successor-in-interest to Chevron Chemical Company,
a party to the Services Agreement, by virtue of a merger agreement; and

          WHEREAS, CCCLLC and Warren have agreed to modify the Services
Agreement as set forth herein.

          NOW THEREFORE, in consideration of the promises and mutual covenants
contained herein and for other good and valuable consideration, the receipt and
sufficiency of which are hereby acknowledged by the parties to this First
Amendment, the parties agree to amend the Services Agreement as follows:

          1. Section 5.0 Term of Exhibit A-5 Barge Transportation is deleted in
its entirety and is replaced by the following new Section 5.0:

                  Notwithstanding the provisions specified in Section 5.0 of
             this Services Agreement, the services covered in this Exhibit shall
             terminate (i) effective August 31, 2003, in the event that WPC does
             not exercise its call option as specified in Section 8.2 of that
             certain Limited Liability Company Agreement between Chevron U.S.A.
             Inc. and Warren Petroleum Company, Limited Partnership, as amended
             (the "LCC Agreement"), or (ii) upon damage beyond the economic
             repair or expiration of the useful life of the barges NATCHEZ and
             COMANCHE, or (iii) as provided in Section 2.2 of this Exhibit. If
             WPC does exercise its call option as specified in Section 8.2 of
             the LLC Agreement on or prior to August 31, 2003, the provisions
             of Section 5.0 of this Services Agreement shall apply, and WPC
             shall be obligated to continue to provide the barge transportation
             services as specified in Section 1.0 of this Exhibit.

          2. This Amendment shall be effective as of August 30, 1998.

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          IN WITNESS WHEREOF, the parties hereto have executed this Amendment as
of the date first above written.

Executed at                           CHEVRON CHEMICAL COMPANY, LLC

1301 McKinney
Houston, TX 77010                     By:  /s/ A. H Uzzell
                                         -----------------------------
                                           Name: A. H Uzzell
                                           Title: Assistant Secretary

Executed at                          WARREN PETROLEUM COMPANY
                                     LIMITED PARTNERSHIP
                                     By:   Warren Petroleum G.P., Inc.,
                                           Its General Partner
1000 Louisiana - Suite 5800
Houston, TX 77002-5050               By: /s/  Stephen A. Furbacher
                                        ------------------------------
                                           Name: S A. Furbacher
                                           Title: President

                                      2<Page>
                                                         Exhibit 10.12(c)

"Pages where confidential treatment has been requested are marked 'Confidential
Treatment Requested.' The redacted material has been separately filed with the
Commission, and the appropriate section has been marked at the appropriate
place and in the margin with a star (*)."

                     AMENDMENT TO CCC/WPC SERVICES AGREEMENT

     THIS Amendment To CCC/WPC Services Agreement (the "Amendment") is made and
entered into this 5th day of January, 2000, by and between Chevron Chemical
Company LLC, a Delaware limited liability company, hereinafter referred to as
"CCC" and Dynegy Midstream Services, Limited Partnership, hereinafter referred
to as "DMSLP". CCC and DMSLP may be referred to collectively as the "Parties"
or singularly as a "Party."

     WHEREAS, CCC's predecessor in interest, Chevron Chemical Company, and
DMSLP, formerly known as Warren Petroleum Company, Limited Partnership, entered
into that certain CCC/WPC Services Agreement (the "Services Agreement")
effective as of September 1, 1996, as amended, pursuant to which CCC and DMSLP
agreed to, among other things, provide certain services to each other; and

     WHEREAS, CCC and DMSLP have agreed to amend and supplement certain portions
of the Services Agreement to add an additional service to be performed by DMSLP
on behalf of CCC by increasing the volumes involved in the service and now
desire to enter into this Second Amendment to evidence such agreement and to
incorporate such changes to the Services Agreement.

     NOW THEREFORE, in consideration of the mutual covenants and agreements
herein contained, CCC and DMSLP agree as follows:

     1.   Effective January 1, 2000, Exhibit "A-3" to the Services Agreement is
          amended and revised by the "Amendment To Exhibit A-3, Galena Park
          Terminalling" attached hereto as Exhibit "A" and made a part hereof.

     2.   Except as specifically set forth herein, the Services Agreement shall
          remain in full force and effect according to its terms.

     IN WITNESS WHEREOF, the Parties hereto have caused this Second Amendment to
be executed by their duly authorized representatives.

DYNEGY MIDSTREAM SERVICES, LIMITED PARTNERSHIP
By: Dynegy Midstream G.P., Inc., its General Partner

By:   /s/  Hunter Battle
   -------------------------------------------
Printed Name:  Hunter Battle
             ---------------------------------
Title:    V.P. West Region Liquids
      ----------------------------------------

CHEVRON CHEMICAL COMPANY LLC

By:      /s/ Charles Loftin
   -------------------------------------------
Printed Name:   Charles Loftin
             ---------------------------------
Title:  Heavy Olefins Prod. Mgr.
      ----------------------------------------

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                       'Confidential Treatment Requested'

                                  EXHIBIT "A"

               AMENDMENT TO EXHIBIT A-3, GALENA PARK TERMINALLING

Effective January 1, 2000, Exhibit A-3 shall be amended as follows:

1.   Under Section 1.2, the volume for Crude Isoprene (C(5)) is hereby
     modified to read as follows:

                 Product                          Estimated Annual Volume
                 -------                          -----------------------

          Crude Isoprene (C(5))                         547,500 BBLS

2.   Section 3.3 shall be revised to read as follows:

     3.3  Crude Isoprene.

          (a)  Transportation of C(5) from CCC's Cedar Bayou Plant through
               Dynegy's eight (8) inch pipeline to the Galena Park Terminal
*              shall be charged a fee of [REDACTED] per gallon. All movements
               of C(5) shall be coordinated through Dynegy's Mont Belvieu
               logistics team. CCC will pump C(5) from the Cedar Bayou Plant
*              through Dynegy's pipeline at a rate no less than [REDACTED]
               barrels per hour.

          (b)  During the initial two (2) year term of this Crude Isoprene
               service, as provided in Section 9.1 below, Dynegy's Tank W20
*              will be utilized to store CCC's C(5). CCC shall lease [REDACTED]
               (the "Base Volume") of C(5) storage capacity from Dynegy at the
*              rate of [REDACTED] per barrel per month. If as of the last day
               of any month CCC's ending inventory of C(5) exceeds the Base
*              Volume, CCC shall pay Dynegy for an additional [REDACTED]
               barrels of storage capacity for the Month in which the Base
*              Amount was exceeded at the rate of [REDACTED] per barrel (i.e.
*              CCC will lease from Dynegy a total of [REDACTED] barrels of
               storage capacity for the Month in which the ending inventory
*              exceeded [REDACTED] barrels).

          (c)  Redelivery of C(5) to CCC or its designee out of Tank W20 into
               tank trucks shall be made between the hours of 7:00 a.m. and
               7:00 p.m., 7 days per week. In addition to the fees set forth in
               this Exhibit, CCC shall pay Dynegy for all operator labor costs
               associated with loading tank trucks. CCC shall also be charged
*              a fee of [REDACTED] per gallon for redeliveries into tank trucks,
               which will be the primary mode for redelivery of C(5). If CCC
               requests redelivery to a customer at GATX, CCC shall be charged a
*              fee of [REDACTED] per gallon and if CCC requests redelivery into
               a pressure

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                       'Confidential Treatment Requested'

*              barge, CCC shall be charged a fee of [REDACTED] per gallon,
               based on an independent inspector's calculation of the volume
               of C(5) loaded onto the barge. CCC will be responsible for all
               transportation costs, including, but not limited to,
               demurrage, tankerman, inspection and surveyor fees.

          (d)  For the purpose of calculating the fees owed by CCC to Dynegy
               for transportation and redeliveries, measurement of the
               volumes of C(5) transported to Dynegy's storage tank shall be
               based on Dynegy's pipeline receipt turbine meter; and,
               measurement of the volumes redelivered by truck shall be based
               on Dynegy's truck rack turbine meter. The Goodyear truck scale
               shall be utilized to verify the turbine meter measurements.
               Barge redeliveries will be billed based on an independent
               inspector's calculation of the volume of C(5) loaded onto the
               barge.

3.   A new sentence will be added at the end of Section 5.3 of Exhibit A-3 to
     read as follows:

          Notwithstanding the foregoing, CCC's option to reinstate the use of
          Tank W20 W1 and W2, as applicable, shall terminate at the end of the
          two year Primary Term, as defined in Section 9.1 of this Exhibit A-3.

4.   A new Section 9.1 is hereby added to Exhibit A-3 to read as follows:

     9.1  Term For Crude Isoprene C(5) Service.

          This Letter Amendment pertaining to Crude Isoprene (C(5)) service
          shall have an initial two year term commencing January 1, 2000 and
*         ending December 31, [REDACTED] (the "Primary Term"), and shall
          continue in effect from calendar quarter to calendar quarter
          thereafter; provided that (i) CCC shall have the right to terminate
          this Letter Amendment and the Crude Isoprene (C(5)) services covered
          hereby effective at the end of the Primary Term or any calendar
          quarter anniversary thereafter by giving Dynegy at least thirty (30)
          days prior written notice of its election to terminate this Letter
          Amendment and (ii) if this Agreement is extended for a period of
*         [REDACTED] beyond the Primary Term (the "Extension Period"), Dynegy
          shall have the right to terminate this Letter Amendment and the Crude
          Isoprene (C(5)) services covered hereby effective at the end of the
          Extension Period or any calendar quarter anniversary thereafter by
          giving CCC at least thirty (30) days prior written notice of its
          election to terminate this Letter Amendment. If, at the end of the
          Primary Term or at any time following the Primary Term, Dynegy has
          the opportunity to secure a third party lease of Tank W20, CCC will
          have the option to match the third party's offer and retain the lease
          of Tank W20 for an equivalent term as set forth in such third party
          offer. If, however, CCC chooses not to match the third party offer,
          Dynegy will offer CCC the right to utilize Tank W1 and/or Tank W2 for
          such Crude Isoprene service. If CCC elects to utilize one or more of
          such Tanks (i) CCC shall advance to Dynegy the cost of connecting the
          Tank(s) for this service, the current costs of which is estimated at
*         [REDACTED], (ii) this lease will cover the Tank(s) selected by CCC
          and (iii) the term of the

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          lease covering the Tank(s) selected by CCC for such Crude Isoprene
          service shall be extended for a term mutually agreed to by the
          Parties.

5.   A new Section 10.1 is hereby added to Exhibit A-3 to read as follows:

     10.1 Indemnity For Crude Isoprene (C(5)) Service

          Notwithstanding and in lieu of the provisions of Section 7.3 of the
          Services Agreement, the following terms and conditions shall apply to
          and only to the services as provided in this Amendment to CCC/WPC
          Services Agreement pertaining to Crude Isoprene (C(5)):

             (a)  Except as provided in (b), DMSLP agrees to indemnify and hold
                  harmless CCC, its officers, directors, employees, agents,
                  contractors and Affiliates from all actual losses, costs,
                  expenses, claims (including, without limitation, personal
                  injury and property damage claims), damages and causes of
                  action, including, without limitation, reasonable attorneys'
                  fees and costs of court incurred by CCC, or paid to third
                  parties by CCC which are caused by (i) the negligence,
                  dishonesty, willful misconduct or gross negligence of DMSLP,
                  its officers, directors, employees, agents, contractors and
                  Affiliates, and its or their performance of the Services
                  and/or (ii) DMSLP's breach of this Agreement.

                  Except as provided in (b), CCC agrees to indemnify and hold
                  harmless DMSLP, its officers, directors, employees, agents,
                  contractors and Affiliates from all actual losses, costs,
                  expenses, claims (including, without limitation, personal
                  injury and property damage claims), damages and causes of
                  action, including, without limitation, reasonable attorneys'
                  fees and costs of court incurred by DMSLP, or paid to third
                  parties by DMSLP which are caused by (i) the negligence,
                  dishonesty, willful misconduct or gross negligence of CCC, its
                  officers, directors, employees, agents, contractors and
                  Affiliates, and its performance of the Services and/or (ii)
                  CCC's breach of this Agreement.

             (b)  CCC shall defend, indemnify and hold harmless DMSLP from and
                  against any and all claims relating to this Agreement for
                  injury to or death of an employee or representative of CCC or
                  its subcontractors, whether or not DMSLP, its employees or
                  representatives are claimed to be passively, concurrently or
                  actively negligent, and regardless of whether liability
                  without fault is imposed or sought to be imposed; provided
                  this indemnity shall not apply when such injury or death is
                  the result of the sole negligence or willful misconduct of
                  DMSLP, its employees or representatives.

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                  DMSLP shall defend, indemnify and hold harmless CCC from and
                  against any and all claims relating to this Agreement for
                  injury to or death of an employee or representative of DMSLP
                  or its subcontractors, whether or not CCC, its employees or
                  representatives are claimed to be passively, concurrently or
                  actively negligent, and regardless of whether liability
                  without fault is imposed or sought to be imposed; provided
                  this indemnity shall not apply when such injury or death is
                  the result of the sole negligence or willful misconduct of
                  CCC, its employees or representatives.

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