UNITED STATES
                             SECURITIES AND EXCHANGE
                                   COMMISSION

                             WASHINGTON, D.C. 20549

                                  SCHEDULE 13D

                    UNDER THE SECURITIES EXCHANGE ACT OF 1934

                          PACIFIC ENERGY PARTNERS, L.P.
                          -----------------------------
                                (Name of Issuer)


                                  COMMON UNITS
                                  ------------
                         (Title of Class of Securities)


                                   69422R 10 5
                                   -----------
                                 (CUSIP Number)

  Thomas R. Denison, First Reserve GP X, Inc., One Lafayette Place, Greenwich,
                        Connecticut 06830 (203) 625-2520
                        --------------------------------
                  (Name, Address and Telephone Number of Person
                Authorized to Receive Notices and Communications)

                                 March 21, 2005
                                 --------------
             (Date of Event which Requires Filing of this Statement)

If the filing person has previously filed a statement on Schedule 13G to report
the acquisition which is the subject of this Schedule 13D, and is filing this
schedule because of Sections 240.13d-1(e), 240.13d-1(f) or 204.13d-1(g), check
the following box. [ ]

NOTE: Schedules filed in paper format shall include a signed original and five
copies of the schedule, including all exhibits. See Section 240.13d-7(b) for
other parties to whom copies are to be sent.

*The remainder of the cover page shall be filled out for a reporting person's
initial filing on this form with respect to the subject class of securities, and
for any subsequent amendment containing information which would alter
disclosures provided in a prior cover page.

The information required on the remainder of this cover page shall not be deemed
to be "filed" for the purpose of Section 18 of the Securities Exchange Act of
1934 ("Act") or otherwise subject to the liabilities of that section of the Act
but shall be subject to all other provisions of the Act (however, see the
Notes).






CUSIP NO.         69422R 10 5
--------------------------------------------------------------------------------
(1)      Names of Reporting Persons
         I.R.S. Identification Nos. of above persons (entities only)

         FIRST RESERVE GP X, INC.           IRS NO. 84-2133571

--------------------------------------------------------------------------------
(2)      Check the Appropriate Box if a Member of a Group (See Instructions)

         (a)  [ ]
         (b)  [X]

--------------------------------------------------------------------------------
(3)      SEC Use Only

--------------------------------------------------------------------------------
(4)      Source of Funds (See Instructions)

         OO
--------------------------------------------------------------------------------
(5)      Check if Disclosure of Legal Proceedings is Required Pursuant to Items
         2(d) or 2(e)

--------------------------------------------------------------------------------
(6)      Citizenship or Place of Organization

         Delaware
--------------------------------------------------------------------------------


Number of                  7.       Sole Voting Power
Shares                              3,143,665(1)
Beneficially               -----------------------------------------------------
Owned by                   8.       Shared Voting Power

Each                       -----------------------------------------------------
Reporting                  9.       Sole Dispositive Power
Person With                         3,143,665 (1)
                           -----------------------------------------------------
                           10.      Shared Dispositive Power

--------------------------------------------------------------------------------

(11)     Aggregate Amount Beneficially Owned by Each Reporting Person
         3,143,665 (1)

--------------------------------------------------------------------------------
(12)     Check if the Aggregate Amount in Row (11) Excludes Certain Shares
         (See Instructions)

--------------------------------------------------------------------------------
(13)     Percent of Class Represented by Amount in Row (11)
         13.7%

--------------------------------------------------------------------------------
(14)     Type of Reporting Person (See Instructions)
         CO

--------------------------------------------------------------------------------

(1) Based on 19,158,747 Common Units, 603,809 General Partner Interests and
3,143,665 Subordinated Units (converted on a one-to-one basis into Common Units
as described in Item 3) outstanding as of February 28, 2005 as reported in the
Issuer's Annual Report on Form 10-K for the year ended December 31, 2004.






CUSIP NO. 69422R 10 5
--------------------------------------------------------------------------------
(1)      Names of Reporting Persons
         I.R.S. Identification Nos. of above persons (entities only)

         FIRST RESERVE GP X, L.P.           IRS NO.  56-2416968

--------------------------------------------------------------------------------
(2)      Check the Appropriate Box if a Member of a Group (See Instructions)
         (a)  [ ]
         (b)  [X]

--------------------------------------------------------------------------------
(3)      SEC Use Only

--------------------------------------------------------------------------------
(4)      Source of Funds (See Instructions)

         OO
--------------------------------------------------------------------------------
(5)      Check if Disclosure of Legal Proceedings is Required Pursuant to Items
         2(d) or 2(e)

--------------------------------------------------------------------------------
(6)      Citizenship or Place of Organization

         Delaware
--------------------------------------------------------------------------------


Number of                  7.       Sole Voting Power
Shares                              3,143,665 (1)
Beneficially               -----------------------------------------------------
Owned by                   8.       Shared Voting Power

Each                       -----------------------------------------------------
Reporting                  9.       Sole Dispositive Power
Person With                         3,143,665 (1)
                           -----------------------------------------------------
                           10.      Shared Dispositive Power

--------------------------------------------------------------------------------
(11)     Aggregate Amount Beneficially Owned by Each Reporting Person
         3,143,665 (1)

--------------------------------------------------------------------------------
(12)     Check if the Aggregate Amount in Row (11) Excludes Certain Shares
         (See Instructions)

--------------------------------------------------------------------------------
(13)     Percent of Class Represented by Amount in Row (11)
         13.7%

--------------------------------------------------------------------------------
(14)     Type of Reporting Person (See Instructions)
         PN

--------------------------------------------------------------------------------

(1) Based on 19,158,747 Common Units, 603,809 General Partner Interests and
3,143,665 Subordinated Units (converted on a one-to-one basis into Common Units
as described in Item 3) outstanding as of February 28, 2005 as reported in the
Issuer's Annual Report on Form 10-K for the year ended December 31, 2004.






CUSIP NO.   69422R 10 5
--------------------------------------------------------------------------------
(1)      Names of Reporting Persons
         I.R.S. Identification Nos. of above persons (entities only)

         FIRST RESERVE PACIFIC HOLDINGS AIV, L.P.         IRS NO.  20-2464499

--------------------------------------------------------------------------------
(2)      Check the Appropriate Box if a Member of a Group (See Instructions)
         (a)  [ ]
         (b)  [X]

--------------------------------------------------------------------------------
(3)      SEC Use Only

--------------------------------------------------------------------------------
(4)      Source of Funds (See Instructions)

         OO
--------------------------------------------------------------------------------
(5)      Check if Disclosure of Legal Proceedings is Required Pursuant to Items
         2(d) or 2(e)

--------------------------------------------------------------------------------

(6)      Citizenship or Place of Organization

         Delaware
--------------------------------------------------------------------------------


Number of                  7.       Sole Voting Power
Shares                              3,143,665 (1)
Beneficially               -----------------------------------------------------
Owned by                   8.       Shared Voting Power

Each                       -----------------------------------------------------
Reporting                  9.       Sole Dispositive Power
Person With                         3,143,665 (1)
                           -----------------------------------------------------
                           10.      Shared Dispositive Power

--------------------------------------------------------------------------------
(11)     Aggregate Amount Beneficially Owned by Each Reporting Person
         3,143,665 (1)

--------------------------------------------------------------------------------
(12)     Check if the Aggregate Amount in Row (11) Excludes Certain Shares
         (See Instructions)

--------------------------------------------------------------------------------
(13)     Percent of Class Represented by Amount in Row (11)
         13.7%

--------------------------------------------------------------------------------
(14)     Type of Reporting Person (See Instructions)
         PN

--------------------------------------------------------------------------------

(1) Based on 19,158,747 Common Units, 603,809 General Partner Interests and
3,143,665 Subordinated Units (converted on a one-to-one basis into Common Units
as described in Item 3) outstanding as of February 28, 2005 as reported in the
Issuer's Annual Report on Form 10-K for the year ended December 31, 2004.






ITEM 1. SECURITY AND ISSUER.

This statement on Schedule 13D (the "Schedule 13D") relates to the common units
representing limited partner interests ("Common Units") of Pacific Energy
Partners, L.P., a Delaware limited partnership (the "Issuer"), into which
subordinated units representing limited partner interests of the Issuer are
convertible (the "Subordinated Units"). The Issuer has its principal executive
offices at 5900 Cherry Avenue, Long Beach, California 90805-4408.

ITEM 2. IDENTITY AND BACKGROUND.

This Schedule 13D is being filed jointly by First Reserve GP X, Inc. ("First
Reserve"), First Reserve GP X, LP ("GP X"), and First Reserve Pacific Holdings
AIV, L.P. ("Holdings LP") (collectively, the "Reporting Persons") to report the
indirect acquisition of Common Units issuable upon the conversion of
Subordinated Units.

First Reserve is the general partner of GP X. GP X is the general partner of
Holdings LP. Following the transaction that is the subject of this Schedule 13D,
Holdings LP directly owns a 30 percent limited partner interest in LB Pacific,
LP ("LB LP") and a 30 percent membership interest in LB Pacific GP, LLC ("LB
LLC").

The Subordinated Units of the Issuer that are the subject of this Schedule 13D
are directly owned by LB LP. LB LLC is the sole general partner of LB LP. LB LP
is the sole limited partner of Pacific Energy GP, LP, which is the sole general
partner of the Issuer. LB LP is also the sole owner of Pacific Energy
Management, LLC, which is the sole general partner of Pacific Energy GP, LP.

The Reporting Persons, by and through the holdings of LB LP and LB LLC, own more
than 5% of the issuable and outstanding Common Units.

Holdings LP is a Delaware limited partnership formed for the purpose of making
investments in the Issuer. GP X is a Delaware limited partnership, the purpose
of which is to act as the general partner of certain investment partnerships,
including Holdings LP. First Reserve is a Delaware corporation and is the
general partner of GP X.

The principal business and office address of the Reporting Persons is One
Lafayette Place, Greenwich, CT 06830.

Information with respect to the executive officers and directors of First
Reserve, including name, business address, present principal occupation or
employment and the organization in which such employment is conducted, and their
citizenship is listed on the attached Schedule I, which is incorporated in this
Schedule 13D by reference.

The Reporting Persons have entered into a Joint Filing Agreement, dated the date
hereof, a copy of which is filed with this Schedule 13D as Exhibit 1 (which is
hereby incorporated by reference) pursuant to which the Reporting Persons have
agreed to file this statement jointly in accordance with the provisions of Rule
13d-1(k)(1) under the Act. Information with respect to each Reporting Person is
given solely by such Reporting Person, and no Reporting Person assumes
responsibility for the accuracy or completeness of the information furnished by
another Reporting Person. The Reporting Persons expressly disclaim that they
have agreed to act as a group other than as described in this Schedule 13D.
Pursuant to Rule 13d-4 of the Act, the Reporting Persons expressly declare that
the filing of this statement shall not be construed as an admission that any
such person is, for the purposes of Section 13(d) and/or Section 13(g) of the
Act or otherwise, the beneficial owner of any securities covered by this
Schedule 13D held by any other person.

During the last five years, none of the Reporting Persons nor any executive
officer or director of First Reserve has (i) been convicted in a criminal
proceeding (excluding traffic violations or similar misdemeanors) or (ii) been a
party to a civil proceeding or a judicial or administrative body of competent
jurisdiction and as a result of such proceeding was or is subject to a judgment,
decree or final order enjoining future violations of, or prohibiting or
mandating activities subject to, federal or state securities laws or finding any
violation with respect to such laws.

ITEM 3. SOURCE AND AMOUNT OF FUNDS OR OTHER CONSIDERATION.

Pursuant to that certain Purchase Agreement, dated March 21, 2005 (the "Purchase
Agreement"), by and among First Reserve Pacific Holdings AIV, L.P. ("Buyer"),
Lehman Sidecar I, LLC and LB I Group Inc. ("Seller"), Buyer agreed to buy and
Seller agreed to sell, approximately 30% of the respective limited partnership
and membership interests of LB LP and LB LLC (the "Acquired Interests"). On
March 21, 2005 (the "Closing"), Buyer acquired (the "Acquisition") all of the
Acquired Interests. LB LP owns 10,465,000 Subordinated Units of the Issuer. The
Subordinated Units may be converted into an equal number of 






Common Units upon satisfaction of the conditions described in the First Amended
and Restated Agreement of Limited Partnership of Pacific Energy Partners, L.P.
dated as of July 26, 2002, as amended by Amendment No. 1 dated as of August 1,
2003, Amendment No. 2 dated as of January 27, 2004, and Amendment No. 3 dated as
of March 26, 2004 (the "Partnership Agreement").

The Buyer paid the Seller approximately $53.8 million in cash at the Closing.
The Buyer financed the $53.8 million in cash entirely through equity
contributions from its limited partners and its general partner.

ITEM 4. PURPOSE OF TRANSACTION.

The purchase by Holdings LP of a 30 percent limited partner interest in LB LP
and a 30 percent membership interest in LB LLC (and resulting indirect
acquisition of beneficial ownership of Subordinated Units and Common Units) was
undertaken for investment purposes. Holdings LP also intends to participate in
and influence the affairs of the Issuer through its rights to appoint directors
to the board of directors of Pacific Energy Management, LLC, a Delaware limited
liability company, which is the general partner of Pacific Energy GP, LP.
Pacific Energy GP, LP is the general partner of the Issuer. The charter
documents of LB LP and LB LLC give Holdings LP limited (in scope and time) veto
rights over certain extraordinary transactions (including mergers and other sale
transactions) at the LB LP and LB LLC level.

Holdings LP intends to review its investment in the Issuer on a continuing basis
and, may or may not acquire additional Units, on the open market or otherwise,
subject to: the price and availability of the Units; subsequent developments
affecting the energy market as a whole; the Issuer and the Issuer's business and
prospects; other investment and business opportunities available to the
Reporting Persons; general stock market and economic conditions; and other
factors. Holdings LP may or may not also decide to dispose of the Units at any
time, including without limitation through adoption and execution of a written
plan under Rule 10b5-1 of the Exchange Act of 1934, or to formulate other
purposes, plans or proposals regarding the Issuer or any of its securities based
on all of the above factors and on the eventual liquidation of Holdings LP in
accordance with its partnership agreement.

Except as set forth in this Item 4, the Reporting Persons do not have any
specific plans or proposals that relate to or would result in any of the actions
specified in clauses (a) through (j) of Item 4 of Schedule 13D.

ITEM 5. INTEREST IN SECURITIES OF THE ISSUER.

(a) -- (b) As of the date hereof, the Reporting Persons do not directly own any
securities of the Issuer. First Reserve is the general partner of GP X. GP X is
the general partner of Holdings LP. Following the transaction that is the
subject of this Schedule 13D, Holdings LP directly owns a 30 percent limited
partner interest in LB LP and a 30 percent membership interest in LB LLC.

The Subordinated Units of the Issuer that are the subject of this Schedule 13D
are directly owned by LB LP and indirectly owned by LB LLC. LB LP directly owns
10,465,000 Subordinated Units.

LB LLC is the sole general partner of LB LP. LB LP the sole limited partner of
Pacific Energy GP, LP, which is the sole general partner of the Issuer. LB LP is
also the sole owner of Pacific Energy Management, LLC, which is the sole general
partner of Pacific Energy GP, LP.

As a result of the above ownership structure, the Reporting Persons may be
deemed to possess sole voting and dispositive powers with respect to 30 percent
of the Subordinated Units directly held by LB LP, which percentage equals
3,143,665.

To the knowledge of the Reporting Persons, no person on Schedule I beneficially
owns any Common Units, General Partner Interests or Subordinated Units.

(c) Other than the transaction described in Item 4, the Reporting Persons have
not effected any transactions during the past 60 days in the Units.

(d) To the best knowledge of the Reporting Persons, no person other than the
Reporting Persons and the limited partners of First Reserve Fund X, LP, an
affiliate of the Reporting Persons, or Holdings LP has the right to receive, or
the power to direct the receipt of dividends from, or the power to direct the
receipt of proceeds of the sale of the Subordinated Units indirectly owned by
the Reporting Persons.






(e) Not applicable.


ITEM 6. CONTRACTS, ARRANGEMENTS, UNDERSTANDINGS OR RELATIONSHIPS WITH RESPECT TO
SECURITIES OF THE ISSUER.

JOINT FILING AGREEMENT

A Joint Filing Agreement dated March 31, 2005, by and among First Reserve
Pacific Holdings AIV, L.P., First Reserve GP X, LP, and First Reserve GP X, Inc.
has been executed by the Reporting Persons, a copy of which is attached hereto
as an exhibit to this Schedule 13D and is incorporated herein by reference.

ISSUER PARTNERSHIP AGREEMENT

Pursuant to the terms of the Issuer's Partnership Agreement, the subordination
period applicable to the Subordinated Units will end once the Issuer meets the
financial tests in its Partnership Agreement, but it generally cannot end before
June 30, 2007. When the subordination period ends, all remaining Subordinated
Units will convert into Common Units on a one-for-one basis. If the Issuer meets
the financial tests in its Partnership Agreement for any quarter ending on or
after June 30, 2005, 25% of the Subordinated Units will convert into Common
Units. If the Issuer meets these tests for any quarter ending on or after June
30, 2006, an additional 25% of the Subordinated Units will convert into Common
Units. The second early conversion of the Subordinated Units may not occur until
at least one year after the first early conversion of Subordinated Units.

PURCHASE AND SALE AGREEMENT

Pursuant to the Purchase Agreement, the Buyer agreed to buy and the Seller
agreed to sell approximately 30 percent of the respective limited partnership
and membership interests of LB LP and LB LLC. The Purchase Agreement is filed as
an exhibit to this Schedule 13D and is incorporated by reference herein and the
description set forth above is qualified in its entirety by reference thereto.

The Issuer Partnership Agreement additionally contains various provisions with
respect to the units governing, among other matters, distributions, transfers
and allocations of profits and losses to the partners. In addition the Issuer GP
and its affiliates have the right to cause the Issuer to register for resale
under the Securities Act of 1933, as amended, and applicable state securities
laws, any limited partner units that they hold. The Issuer is obligated to pay
all expenses incidental to the registration, excluding underwriting discounts
and commission.

ITEM 7. MATERIAL TO BE FILED AS EXHIBITS

    1.  Joint Filing Agreement of Schedule 13D. (1)

    2.  Purchase Agreement, dated as of March 21, 2005.(1)

    3.  First Amended and Restated Agreement of Limited Partnership of Pacific
        Energy Partners, L.P., dated July 26, 2002 (filed as Exhibit 3.2 to the
        Issuer's Form 10-Q filed on September 5, 2002), as amended by Amendment
        No. 1 to First Amended and Restated Agreement of Limited Partnership of
        the Issuer dated August 1, 2003 (filed as Exhibit 3.3 to the Issuer's
        Form S-3 filed on August 1, 2003), as amended by Amendment No. 2 to
        First Amended and Restated Agreement of Limited Partnership of Pacific
        Energy Partners, L.P., dated January 27, 2004 (filed as Exhibit 3.4 to
        the Issuer's Form 10-K filed March 15, 2005), as amended by Amendment
        No. 3 to First Amended and Restated Agreement of Limited Partnership of
        Pacific Energy Partners, L.P. (filed as Exhibit 3.1 to the Issuer's Form
        10-Q on May 5, 2004).

(1) Filed herewith






                                    SIGNATURE


After reasonable inquiry and to the best of my knowledge and belief, I certify
that the information set forth in this statement is true, complete and correct.

DATED AS OF MARCH 31, 2005


                                                    
First Reserve GP X, Inc.                               First Reserve GP X, LP
                                                       By: First Reserve GP X, Inc., its General Partner


By: /s/ Thomas R. Denison                              By: /s/ Thomas R. Denison
    ----------------------------------------               ----------------------------------------
    Thomas R. Denison, Managing Director                   Thomas R. Denison, Managing Director


First Reserve Pacific Holdings AIV, LP
By: First Reserve GP X, L.P., its General Partner
By: First Reserve GP X, Inc., its General Partner


By: /s/ Thomas R. Denison
    ----------------------------------------
    Thomas R. Denison, Managing Director







                                   SCHEDULE I


The name, business address and present principal occupation or employment of
each of the executive officers and directors of First Reserve GP X, Inc. are set
forth below. Each such person is a citizen of the United States and does not
have any other principal occupation:




Name                                         Position with First Reserve GP X, Inc.              Business Address
-----------------------------------------    ------------------------------------------------    -----------------------
                                                                                           
William E. Macaulay                          Chairman, CEO, Managing Director and Member of      (1)
                                             the Board of Directors

John A. Hill                                 Vice Chairman, Managing Director                    (1)

Ben A. Guill                                 President, Managing Director and Member of the      (2)
                                             Board of Directors

Thomas J. Sikorski                           Managing Director                                   (1)

J.W.G. (Will) Honeybourne                    Managing Director                                   (2)

Thomas R. Denison                            Managing Director, General Counsel, Secretary       (1)

Alex T. Krueger                              Managing Director                                   (1)

Jennifer C. Zarrilli                         Treasurer, Chief Financial Officer and Member of    (1)
                                             the Board of Directors



(1) One Lafayette Place, Third Floor, Greenwich, CT 06830

(2) 600 Travis Street, Suite 6000, Houston, TX 77002







                                 EXHIBIT INDEX



     
    1.  Joint Filing Agreement of Schedule 13D.(1)

    2.  Purchase Agreement, dated as of March 21, 2005.(1)

    3.  First Amended and Restated Agreement of Limited Partnership of Pacific
        Energy Partners, L.P., dated July 26, 2002 (filed as Exhibit 3.2 to the
        Issuer's Form 10-Q filed on September 5, 2002), as amended by Amendment
        No. 1 to First Amended and Restated Agreement of Limited Partnership of
        the Issuer dated August 1, 2003 (filed as Exhibit 3.3 to the Issuer's
        Form S-3 filed on August 1, 2003), as amended by Amendment No. 2 to
        First Amended and Restated Agreement of Limited Partnership of Pacific
        Energy Partners, L.P., dated January 27, 2004 (filed as Exhibit 3.4 to
        the Issuer's Form 10-K filed March 15, 2005), as amended by Amendment
        No. 3 to First Amended and Restated Agreement of Limited Partnership of
        Pacific Energy Partners, L.P. (filed as Exhibit 3.1 to the Issuer's Form
        10-Q on May 5, 2004).



(1) Filed herewith