FIRST AMENDMENT TO CREDIT AGREEMENT AND GUARANTEE AND COLLATERAL AGREEMENT

Exhibit 10.6

FIRST AMENDMENT

TO

CREDIT AGREEMENT

AND

GUARANTEE AND COLLATERAL AGREEMENT

dated as of

July 25, 2007

among

GENESIS CRUDE OIL, L.P.,

as the Borrower,

GENESIS ENERGY, L.P.,

as the Parent and a Guarantor,

and

the Lenders, Issuing Banks and Guarantors Party Hereto

FORTIS CAPITAL CORP.,

as Administrative Agent,

DEUTSCHE BANK SECURITIES INC.,

as Syndication Agent,

and

BANK OF AMERICA, N.A.,

U.S. BANK NATIONAL ASSOCIATION,

WACHOVIA BANK, NATIONAL ASSOCIATION,

BMO CAPITAL MARKETS FINANCING, INC.,

ROYAL BANK OF CANADA, and

SUNTRUST BANK,

as Co-Documentation Agents

TABLE OF CONTENTS

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FIRST AMENDMENT TO CREDIT AGREEMENT AND GUARANTEE AND

COLLATERAL AGREEMENT

THIS FIRST AMENDMENT TO CREDIT AGREEMENT AND GUARANTEE AND COLLATERAL AGREEMENT (this “ First Amendment ”) dated as of July 25, 2007, is by and among GENESIS CRUDE OIL, L.P., a Delaware limited partnership (the “ Borrower ”), GENESIS ENERGY, L.P., a Delaware limited partnership (the “ Parent ”), FORTIS CAPITAL CORP., as administrative agent (in such capacity, together with its successors in such capacity, the “ Administrative Agent ”) for the lenders party to the Credit Agreement referred to below (collectively, the “ Lenders ”), and the undersigned Guarantors and Lenders.

R E C I T A L S

A.(i) The Borrower, the Parent, the Lenders, the Administrative Agent and the other agents referred to therein are parties to that certain Credit Agreement dated as of November 15, 2006 (as amended, supplemented or otherwise modified from time to time prior to the date hereof, the “ Credit Agreement ”), pursuant to which the lenders party thereto have made certain Loans and provided certain Commitments (subject to the terms and conditions thereof) to the Borrower and (ii) the Borrower, the Guarantors signatory thereto and the Administrative Agent are party to that certain Guarantee and Collateral Agreement dated as of November 15, 2006 (as amended, supplemented or otherwise modified from time to time prior to the date hereof, the “ Guarantee and Collateral Agreement ”).

B. In connection with the Davison Acquisition (as defined below), the Parent has entered into the Davison Contribution and Sale Agreement (as defined below) pursuant to which it will acquire the assets and entities, and enter into the other transactions therein described.

C. The Borrower has formed a new Restricted Subsidiary, Genesis Alabama Pipeline, LLC, an Alabama limited liability company (“ Genesis Alabama ”), that as of the First Amendment Effective Date will not hold significant Real Property.

D. The Parent and the Borrower wish, and the Lenders signatory hereto and the Administrative Agent are willing, (i) to amend the Credit Agreement to increase the aggregate Committed Amount to $500,000,000, to be utilized in part to pay Acquisition Consideration in connection with the Davison Acquisition, (ii) to consent to the delay by the Borrower and the Parent in meeting the Section 5.10 Timing Requirements (as defined below) in respect of Genesis Alabama Real Property (as defined below) and waive compliance with Section 5.10 with respect to certain Arkansas Real Property (as defined below) and (iii) to further amend the Credit Agreement and to amend the Guarantee and Collateral Agreement in connection therewith.

NOW, THEREFORE, in consideration of the premises and the mutual covenants herein contained, for good and valuable consideration, the receipt and sufficiency of which are hereby acknowledged, the parties hereto agree as follows:

Section 1. Defined Terms . Each capitalized term used herein but not otherwise defined herein has the meaning given such term in the Credit Agreement. Unless otherwise indicated, all

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article, schedule, exhibit and section references in this First Amendment refer to articles and sections of the Credit Agreement.

As used in this First Amendment, the following terms shall have the meanings specified below:

“ Acquired Companies ” has the meaning assigned to such term in the Davison Contribution and Sale Agreement.

“ Additional Guarantors ” means, collectively, Genesis Davison, LLC, a Delaware limited liability company, TDC Energy Services, Inc., a Delaware corporation, TDC Refinery Services Corp., Inc., a Delaware corporation, TDC Services Corporation, Inc., a Delaware corporation, Davison Petroleum Supply, LLC, a Delaware limited liability company, Davison Transportation Services, LLC, a Delaware limited liability company, Red River Terminals, L.L.C., a Louisiana limited liability company, Red River Terminals, L.L.C., a Delaware limited liability company, Davison Corp., Inc., a Delaware corporation, Fuel Masters, LLC, a Texas limited liability company, TDC, L.L.C., a Louisiana limited liability company, and Genesis TDC Texas, LLC, a Texas limited liability company, and “ Additional Guarantor ” shall have the correlative meaning.

“ Arkansas Real Property ” means Real Property of the Borrower Parties located in the State of Arkansas.

“ Davison Acquisition ” means the acquisition by the Parent or its designees (subject to Section 5.4(ii) of this First Amendment) of, inter alia , the Subject Assets.

“ Davison Acquisition Documents ” means, collectively, the Davison Contribution and Sale Agreement and all schedules, exhibits and annexes thereto and all side letters and agreements affecting the terms thereof or entered into in connection therewith.

“ Davison Contribution and Sale Agreement ” means the Contribution and Sale Agreement by and among Davison Petroleum Products, L.L.C., Davison Transport, Inc., Transport Company, Davison Terminal Service, Inc., Sunshine Oil & Storage, Inc., T&T Chemical, Inc., Fuel Masters, LLC, TDC, L.L.C. and Red River Terminal, L.L.C., as Sellers and Parent as Buyer, dated as of April 25, 2007, as amended by Amendment No. 1 thereto dated as of July 25, 2007.

“ First Amendment Effective Date ” has the meaning assigned to such term in Section 4 hereof.

“ First Amendment Effective Date Real Property Requirements ” means the following:

(a) with respect to each applicable Mortgaged Property:

(i) a Mortgage encumbering each such Mortgaged Property in favor of the Administrative Agent, for the benefit of the Secured Parties, duly executed and acknowledged by each Borrower Party that is the owner of or holder of any

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interest in such Mortgaged Property, and otherwise in form for recording in the recording office of each applicable political subdivision where each such Mortgaged Property is situated, together with such certificates, affidavits, questionnaires or returns as shall be required in connection with the recording or filing thereof to create a lien under applicable Governmental Requirements, and such financing statements and any other instruments necessary to grant a mortgage lien under the laws of any applicable jurisdiction, all of which shall be in form and substance reasonably satisfactory to Administrative Agent;

(ii) with respect to each such Mortgaged Property, such consents, approvals, amendments, supplements, estoppels, tenant subordination agreements or other instruments as shall reasonably be deemed necessary by the Administrative Agent in order for the owner or holder of the fee or leasehold interest constituting such Mortgaged Property to grant the Lien contemplated by the Mortgage with respect to such Mortgaged Property; and

(iii) with respect to each such Mortgage, opinions of local counsel to the Borrower Parties, which opinions (A) shall be addressed to the Administrative Agent and each of the Lenders and be dated the First Amendment Effective Date, (B) shall cover the enforceability of the respective Mortgage and such other matters incident to the transactions contemplated herein as the Administrative Agent may reasonably request and (C) shall be in form and substance reasonably satisfactory to the Administrative Agent.

(b) evidence reasonably acceptable to the Administrative Agent of payment by a Borrower Party of all search and examination charges, escrow charges and related charges, mortgage recording taxes, fees, charges, costs and expenses required for the recording of the Mortgages referred to above;

(c) with respect to each such Mortgaged Property, the Parent and each Restricted Subsidiary shall have made all notifications, registrations and filings, to the extent required by, and in accordance with, all Governmental Real Property Disclosure Requirements applicable to such Mortgaged Property;

(d) to the extent requested by the Administrative Agent, (i) ALTA mortgagee title insurance policies or unconditional commitments therefor with extended coverage guaranteeing over the standard exceptions to title customarily contained in such policies, survey exceptions, parties in possession exception, and mechanic’s and materialman’s lien exceptions, issued by one or more title companies reasonably satisfactory to the Administrative Agent with respect to each such Mortgaged Property that is material to the Borrower’s Business and constitutes interests owned in “fee” (each, a “ Title Policy ”), in amounts not less than the fair market value of each such Mortgaged Property, together with a title report issued by a title company with respect thereto, dated not more than thirty (30) days prior to the First Amendment Effective Date and copies of all recorded documents listed as exceptions to title or otherwise referred to therein, each in form and substance reasonably satisfactory to the Administrative Agent and (ii) evidence

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satisfactory to the Administrative Agent that such Borrower Party has paid to the title company or to the appropriate governmental authorities all expenses and premiums of the title company and all other sums required in connection with the issuance of each Title Policy; and

(e) to the extent requested by the Administrative Agent, ALTA surveys of all such Mortgaged Properties (other than Pipelines) that are material to the Borrower’s Business and on which improvements are located, in form and substance satisfactory to Administrative Agent, certified to the Administrative Agent and dated not more than thirty (30) days prior to the First Amendment Effective Date.

“ First Amendment Foreign Subsidiaries ” means TDC Peru, TDC Energy Canada and TDC Chile.

“ First Amendment Unrestricted Subsidiaries ” means the First Amendment Foreign Subsidiaries, International Holdco and South America Holdco.

“ Genesis Alabama ” has the meaning assigned to such term in the Recitals hereto.

“ Genesis Alabama Pipeline Project ” means the crude oil gathering system to be constructed in the Little Cedar Creek Field in Conecuh County, Alabama and the crude oil pipeline systems connecting such crude oil gathering system to the Genesis Pipeline USA Florida Pipeline System at a point in Escambia County, Alabama.

“ Genesis Alabama Real Property ” means all Real Property of Genesis Alabama.

“ Genesis Alabama Real Property Compliance Date ” has the meaning assigned to such term in Section 2.18(a)(i) hereof.

“ International Holdco ” means TDC Americas, LLC, a Delaware limited liability company.

“ Port Hudson Acquisition ” means the acquisition by Genesis Crude Oil, L.P., of, inter alia , the Port Hudson Assets.

“ Port Hudson Assets ” has the meaning assigned to such term in the Port Hudson Purchase Agreement.

“ Port Hudson Purchase Agreement ” means the Port Hudson Purchase Agreement between BP Pipelines (North America) Inc., as Seller, and Genesis Crude Oil, L.P., as Buyer, dated May 23, 2007.

“ Section 5.10 Timing Requirements ” means the timing requirements set forth in Section 5.10 pertaining to the documentation, collateral and other requirements set forth therein, which timing requirements state that such documentation, collateral and other requirements set forth in Section 5.10 must be complied with promptly, by a certain specified date or within a certain specified time period after a Restricted Subsidiary’s acquisition of assets.

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“ South America Holdco ” means TDC South America, LLC, a Delaware limited liability company.

“ Subject Assets ” has the meaning assigned to such term in the Davison Contribution and Sale Agreement.

“ TDC Chile ” means an entity to be formed as a (direct or indirect) Subsidiary of International Holdco and/or South America Holdco under the laws of Chile.

“ TDC Energy Canada ” means 0790683 B.C. Ltd., a Canadian company.

“ TDC Peru ” means TDC Peru S.A.C., a Peruvian company.

Section 2. Amendments to Credit Agreement .

2.1 Amendments to Section 1.01 (Defined Terms).

(a) The definition of “ Agreement ” is hereby amended and restated in its entirety to read as follows:

“ Agreement ” means this Credit Agreement, as amended by the First Amendment, as the same may from time to time be amended, modified, restated, or replaced from time to time, and any annexes, exhibits and schedules to any of the foregoing.

(b) The definition of “ Committed Amount ” is hereby amended by amending and restating the penultimate sentence thereof to read in its entirety as follows:

The aggregate Committed Amount as of the First Amendment Effective Date shall be $500,000,000.

(c) The definition of “ Consolidated EBITDA ” is hereby amended by adding the words “including all expense recorded for the Parent’s stock appreciation rights plan in excess of cash payments for exercised rights” immediately following the words “any non-cash stock or stock option or similar compensation expense,” in clause (iv) thereof.

(d) The definition of “ Material Acquisition ” is hereby deleted and replaced in its entirety to read as follows:

“ Material Acquisition ” means a Permitted Acquisition that, when taken together with all other Permitted Acquisitions that have been consummated in the immediately prior twelve months (but not counting any Permitted Acquisition consummated prior to the beginning of the most recently commenced Borrowing Base Multiple Increase Period), collectively have an aggregate Acquisition Consideration in excess of $75,000,000.

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(e) Clause (d) of the definition of “ Permitted Encumbrances ” is hereby deleted and replaced in its entirety to read as follows:

(d) deposits to secure the performance of bids, trade contracts, leases, statutory obligations, surety and appeal bonds in an amount not to exceed $3,000,000, performance bonds and other obligations of a like nature, in each case in the ordinary course of business;

(f) The definition of “ Substantial Transaction ” is hereby deleted and replaced in its entirety to read as follows:

“ Substantial Transaction ” means any Permitted Acquisition or Divestiture in respect of which the aggregate Acquisition Consideration (or, in the case of a Divestiture, the consideration paid by the purchaser if calculated in the same manner as the definition of Acquisition Consideration) is in excess of $25,000,000.

(g) The definition of “Test Period” is hereby deleted and replaced in its entirety to read as follows:

“ Test Period ” means each period of four consecutive fiscal quarters of the Borrower then last ended, in each case taken as one accounting period; provided that when used in this Agreement in connection with a Substantial Transaction being consummated after the end of a fiscal quarter but prior to the date for which financial statements have been delivered to the Lenders for such fiscal quarter, it shall mean the Calculation Period (without giving effect to this proviso).

(h) The definition of “Transactions” is hereby deleted and replaced in its entirety to read as follows:

“ Transactions ” means the execution, delivery and performance by the Borrower and the Parent of this Agreement (including for the avoidance of doubt any amendments, modifications, supplements or restatements thereof), the borrowing of Loans, the use of the proceeds thereof (including to refinance loans under the Existing Credit Agreement and to pay Acquisition Consideration for any Permitted Acquisition) and the issuance of Letters of Credit hereunder, and the execution, delivery and performance of the other Loan Documents by the Borrower Parties.

(i) The following definitions are hereby added where alphabetically appropriate to read as follows:

“ Additional Guarantors ” has the meaning assigned to such term in the First Amendment.

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“ Davison Acquisition ” has the meaning assigned to such term in the First Amendment.

“ Davison Contribution and Sale Agreement ” has the meaning assigned to such term in the First Amendment.

“ Davison Information Memorandum Materials ” means the information memorandum and the other written information distributed by the Borrower in connection with the bank meeting on or about June 15, 2007.

“ First Amendment ” means the First Amendment to Credit Agreement dated as of July 25, 2007 among the Borrower, the Parent, the Administrative Agent, the Lenders party thereto, and the other agents and parties thereto.

“ First Amendment Effective Date ” has the meaning assigned to such term in the First Amendment.

“ Port Hudson Acquisition ” has the meaning assigned to such term in the First Amendment.

2.2 Amendment to Section 2.06(b) (Letters of Credit) . Section 2.06(b) is hereby amended by deleting the dollar amount “$50,000,000” in the last sentence thereof and replacing it with the dollar amount $100,000,000”.

2.3 Amendment to Section 5.10(a) (Additional Collateral; Additional Guarantors).

(a) Section 5.10(a) of the Credit Agreement is hereby amended by deleting the dollar amount “$5,000,000” in the first parenthetical therein and replacing it with the dollar amount “$10,000,000”.

(b) Clause (ii) of Section 5.10(a) of the Credit Agreement is hereby deleted and replaced in its entirety to read as follows:

(ii) grant or cause to be granted to the Administrative Agent for the benefit of the Secured Parties a First Priority Lien of record on all such Equity Interests, Real Property, Pipelines and Property (other than such Equity Interests, Real Property, Pipelines and Property encumbered by prior Liens in existence at the time of the acquisition thereof and not created in anticipation of such acquisition, in which case the Lien of the Administrative Agent for the benefit of the Secured Parties shall be of such priority as is permitted by such prior Lien), upon terms substantially the same as those set forth in the Security Documents for Property of a similar type, and complete such other actions as would have been necessary to satisfy the conditions set forth in Section 4.01 of this Agreement or in the definition of First Amendment Effective Date Real Property Requirements (as defined in the First Amendment) had such Property been owned thereby on the date of this Agreement or the First Amendment, as applicable.

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2.4 Amendment to Section 6.01(e) (Indebtedness) . Section 6.01(e) of the Credit Agreement is hereby deleted and replaced in its entirety to read as follows:

(e) Guarantees by any Borrower Party of up to (i) an aggregate of $7,500,000 of Indebtedness of the Sandhill Joint Venture outstanding at any time, and (ii) an additional aggregate $10,000,000 of Indebtedness of one or more Joint Ventures, including the Sandhill Joint Venture, outstanding at any time;

2.5 Amendment to Section 6.01(g) (Indebtedness) . Section 6.01(g) of the Credit Agreement is hereby deleted and replaced in its entirety to read as follows:

(g) Indebtedness of any Borrower Party owing in connection with deferred payments of insurance premiums; provided that all such Indebtedness of all Borrower Parties shall not exceed $15,000,000 outstanding at any one time;

2.6 Amendment to Section 6.01(h) (Indebtedness) . Section 6.01(h) of the Credit Agreement is hereby deleted and replaced in its entirety to read as follows:

(h) Indebtedness not to exceed $20,000,000 in the aggregate outstanding at any one time consisting of Non-Recourse Obligations of a Restricted Subsidiary assumed by such Restricted Subsidiary in connection with any Acquisition permitted pursuant to Section 6.05 (or, if such Restricted Subsidiary is acquired as part of such Acquisition, existing prior thereto); provided that such Indebtedness exists at the time of such Acquisition at least in the amounts assumed in connection therewith and is not drawn down, created or increased in contemplation of or in connection with or subject to such Acquisition;

2.7 Amendment to Section 6.02(f) (Liens) . Section 6.02(f) of the Credit Agreement is hereby amended by deleting the dollar amount “$1,000,000” in clause (iv) thereof and replacing it with the dollar amount “$10,000,000”.

2.8 Amendment to Section 6.03(b) (Fundamental Changes; Limitations on Business; Limited Purpose of the Parent) . Section 6.03(b) of the Credit Agreement is hereby deleted and replaced in its entirety to read as follows:

(b) It will not and will not permit any of its subsidiaries or Joint Ventures to engage to any material extent in any business other than (i) refining services, gathering, transporting (by barge, pipeline, ship, truck or other modes of transportation), terminalling, storing, producing, acquiring, developing, exploring for, processing, dehydrating, marketing, trading, fractionating and otherwise handling hydrocarbons (including crude oil, natural gas, condensate, natural gas liquids, liquefied natural gas, and refined petroleum products), sulfur, sodium chloride, carbon dioxide, sodium hydrosulfide and caustic soda, including constructing pipeline, platform, dehydration, processing and other related facilities, activities, services or derivative products related or ancillary thereto, (ii)

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businesses of the type conducted by it and its subsidiaries and Joint Ventures as of the date of the First Amendment and businesses reasonably related thereto, (iii) bulk commodity transportation that the Sellers or the Acquired Companies (each as defined in the Davison Contribution and Sale Agreement) have historically transported and (iv) any other businesses as long as the consolidated total assets principally relating to such other businesses, taken together, would not constitute greater than 5% of consolidated total assets.

2.9 Amendment to Section 6.04(g) (Investments, Loans, Advances, and Guarantees) . Section 6.04(g) of the Credit Agreement is hereby deleted and replaced in its entirety to read as follows:

(g) Investments in Permitted Joint Ventures or Unrestricted Subsidiaries (in addition to the Investments described in clause (b) above), in an amount not to exceed $10,000,000 in the aggregate during the term of this Agreement.

2.10 Amendment to Section 6.06(h) (Sale of Assets) . Section 6.06(h) of the Credit Agreement is hereby amended by deleting the dollar amount “$2,000,000” in the proviso thereto and replacing it with the dollar amount “$10,000,000”.

2.11 Amendment to Section 6.12 (Creation of Subsidiaries) . Clause (c) of Section 6.12 of the Credit Agreement is hereby deleted and amended in its entirety to read as follows:

(c) any Foreign Subsidiary (other than the First Amendment Foreign Subsidiaries (as such term is defined in the First Amendment)) without the prior written consent of the Required Lenders.

2.12 Amendment to Section 6.13 (Limitation on Leases) . Section 6.13 of the Credit Agreement is hereby amended by deleting the dollar amount “$10,000,000” therein and replacing it with the dollar amount “$25,000,000”.

2.13 Amendment to Section 6.18 (Control Agreements) . Section 6.18 of the Credit Agreement is hereby deleted and replaced in its entirety to read as follows:

Neither it nor any of its Restricted Subsidiaries shall open any deposit account, securities account or commodities account without subjecting such account to a First Priority Lien in favor of the Administrative Agent for the benefit of the Secured Parties, pursuant to a Control Agreement in form and substance satisfactory to the Administrative Agent; provided , that the Borrower shall be permitted to maintain the operating accounts set forth on Schedule 6.18 without subjecting such accounts to the requirements of this Section 6.18, subject to the conditions and requirements set forth on such Schedule.

2.14 Amendment to Section 6.23 (Excess Cash) . Section 6.23 of the Credit Agreem