JOINDER AND FOURTH AMENDMENT TO CREDIT AGREEMENT

Exhibit 10.13

JOINDER AND FOURTH AMENDMENT TO CREDIT AGREEMENT

This Joinder and Fourth Amendment to Credit Agreement (this “Amendment”) is entered into as of the 1st day of April, 2011 (the “Amendment Effective Date”), by and among NGL ENERGY PARTNERS LP, a Delaware limited partnership (“Parent”), SILVERTHORNE OPERATING LLC, a Delaware limited liability company (“Silverthorne”), each subsidiary of Silverthorne listed as a “Borrower” on the signature pages hereto (together with Silverthorne, each a “Borrower”, and collectively, the “Borrowers”), WELLS FARGO BANK, NATIONAL ASSOCIATION, as agent (the “Agent”) for the Lenders (defined below), and the Additional Revolving Lender (defined below).

RECITALS

WHEREAS, the Credit Parties, the Agent, and the financial institutions party thereto (the “Lenders”) have executed that certain Credit Agreement dated as of October 14, 2010 (as such may be amended, modified and supplemented from time to time, the “Credit Agreement”), and the Credit Parties; unless otherwise defined herein, all capitalized terms not defined herein have the meaning given such terms in the Credit Agreement;

WHEREAS, the Borrowers have requested an increase in the Total Acquisition Revolving Commitment pursuant to Section 2.4(c) of the Credit Agreement and have obtained an additional Commitment in the aggregate totaling $20,000,000 (the “Commitment Increase”) from PNC Bank, National Association (the “Additional Revolving Lender”);

WHEREAS, the Agent, the Swingline Lender, and each Issuing Bank have separately approved the joinder of the Additional Revolving Lender to the Credit Agreement as a new Revolving Lender as required by Section 2.4(c) of the Credit Agreement;

WHEREAS, the Credit Parties and the Additional Revolving Lender have requested the Agent agree to amend the Credit Agreement as set forth herein and in accordance with Section 2.4(d) of the Credit Agreement; and

WHEREAS, the Agent is willing to amend the Credit Agreement as set forth herein, subject to the terms and conditions contained herein.

NOW THEREFORE, in consideration of the premises and mutual covenants herein contained and intending to be legally bound hereby, the parties hereby agree as follows:

Section 1.               Joinder of Additional Revolving Lender.

1.1.          Joinder.  The Additional Revolving Lender hereby joins in, becomes a party to, and agrees to comply with and be bound by the terms and conditions of the Credit Agreement as a Revolving Lender thereunder and under each and every other Loan Document to which any Revolving Lender is required to be bound by the Credit Agreement, to the same extent as if the Additional Revolving Lender were an original signatory thereto.  The Additional Revolving Lender hereby appoints and authorizes the Agent to take such action as agent on its behalf and to

exercise such powers and discretion under the Credit Agreement as are delegated to the Agent by the terms thereof, together with such powers and discretion as are reasonably incidental thereto.  The Additional Revolving Lender represents and warrants that (a) it has full power and authority, and has taken all action necessary, to execute and deliver this Amendment, to consummate the transactions contemplated hereby and to become a Lender under the Credit Agreement, (b) it has received a copy of the Credit Agreement and copies of the most recent financial statements delivered pursuant to Section 6.3 thereof, and such other documents and information as it has deemed appropriate to make its own credit analysis and decision to enter into this Amendment and to become a Revolving Lender on the basis of which it has made such analysis and decision independently and without reliance on the Agent or any other Revolving Lender, and (c) from and after the Amendment Effective Date, it shall be a party to and be bound by the provisions of the Credit Agreement and the other Loan Documents and have the rights and obligations of a Revolving Lender thereunder as if it had executed the Credit Agreement and the other Loan Documents.

1.2.          Reaffirmation of Obligations.  Each Credit Party hereby acknowledges, agrees and confirms that, by its execution of this Amendment it accepts the Additional Revolving Lender as a Revolving Lender for all purposes of the Credit Agreement and reaffirms its Obligations to the Lenders (including the Additional Revolving Lender) under the Credit Agreement and the other Loan Documents.

Section 2.               Amendments to Schedule 1.1A of the Credit Agreement.  In reliance upon the representations, warranties, covenants and conditions contained in this Amendment, Schedule 1.1A to the Credit Agreement is amended and restated in its entirety by Schedule 1.1A attached hereto.  After giving effect to this Amendment and any Loans made on the Amendment Effective Date, (a) each Lender who holds Loans in an aggregate amount less than its Commitment Percentage (after giving effect to this Amendment) of all Loans shall advance new Loans that shall be disbursed to the Agent and used to repay Loans outstanding to each Lender who holds Loans in an aggregate amount greater than its Commitment Percentage of all Loans, (b) each Lender’s participation in each Letter of Credit, if any, shall be automatically adjusted to equal its Commitment Percentage (after giving effect to this Amendment), and (c) such other adjustments shall be made as the Agent shall specify so that (i) each Lender’s Acquisition Revolving Exposure equals its Acquisition Revolving Commitment Percentage (after giving effect to this Amendment) of the aggregate Acquisition Revolving Loans of all Lenders, and (ii) each Lender’s Working Capital Revolving Exposure equals its Working Capital Revolving Commitment Percentage (after giving effect to this Amendment) of the aggregate Working Capital Revolving Loans of all Lenders.

Section 3.               Conditions Precedent to Amendment.  This Amendment will be effective as of the Amendment Effective Date, on the condition that the following conditions precedent will have been satisfied:

3.1.          Amendment.  The Agent will have received counterparts of this Amendment executed on behalf of the Credit Parties, the Agent, and the Additional Revolving Lender.

3.2.          Certificates.  The Borrowers shall have delivered to the Agent a certificate of each Credit Party (in sufficient copies for each Lender) signed by an authorized officer of such

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Credit Party (a) certifying and attaching the resolutions adopted by such Credit Party approving or consenting to the Commitment Increase, and (b) certifying that, before and after giving effect to the increase (i) the representations and warranties contained in Section 5 of the Credit Agreement and the other Loan Documents are true and correct, except to the extent that such representations and warranties specifically refer to an earlier date, in which case they are true and correct as of such earlier date, and (ii) no Default or Event of Default exists.

3.3.          Return of Existing Notes; Execution of New Notes.  Each Revolving Lender that has received a Note shall have returned such Note to the Agent for reissuance in order to reflect the reallocated Commitments and Revolving Loans.  The Borrowers shall have executed and delivered to the Agent new Notes in exchange for such surrendered Notes in amounts reflecting the reallocated Commitments and Revolving Loans.

3.4.          Fees.  The Borrowers shall have paid on or before the Amendment Effective Date all fees owed to the Additional Revolving Lender by the Borrowers under any commitment letters or fee letters entered into between the Borrowers or any of their Affiliates and the Additional Revolving Lender.

Section 4.               Representations, Warranties, and Covenants of the Credit Parties.  To induce the Agent and the Additional Revolving Lender to enter into this Amendment, each of the Credit Parties hereby represents, warrants, and covenants to the Agent and the Additional Revolving Lender as follows:

4.1.          Due Authorization; No Conflict.  The execution, delivery and performance by the Credit Parties of this Amendment are within each Credit Party’s limited liability company or partnership powers (as applicable), have been duly authorized by all necessary action, require no action by or in respect of, or filing with, any governmental body, agency or official and do not violate, conflict with, or constitute a default under any Legal Requirement, the Organizational Documents of any Credit Party, or any material contract binding upon any of the Credit Parties, or result in the creation or imposition of any Lien upon any of the assets of any of the Credit Parties.

4.2.          Validity and Enforceability.  This Amendment constitutes the valid and binding obligation of each of the Credit Parties enforceable in accordance with its terms, except as the enforceability thereof may be limited by bankruptcy, insolvency, fraudulent conveyance or transfer, moratorium or similar laws affecting creditors’ rights generally, and general equitable principles including remedies of specific performance and injunction.

4.3.          No Defenses.  None of the Credit Parties has any defenses to payment, counterclaims, or right of set-off with respect to any Obligations existing as of the Amendment Effective Date.

Section 5.               Miscellaneous.

5.1.          Reaffirmation of Loan Documents.  Any and all of the terms and provisions of the Credit Agreement and the Loan Documents will, except as amended and modified hereby, remain in full force and effect.  The amendments contemplated hereby shall not limit or impair

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any Liens securing the Obligations, each of which are hereby ratified and affirmed.  This Amendment constitutes a Loan Document.

5.2.          Parties in Interest.  All of the terms and provisions of this Amendment will bind and inure to the benefit of the parties to the Credit Agreement and their respective successors and assigns.

5.3.          Expenses.  As provided in Section 10.9 of the Credit Agreement, the Borrowers hereby agree to pay on demand all legal and other fees, costs and expenses incurred by the Agent in connection with the negotiation, preparation, and execution of this Amendment and all related documents.

5.4.          Counterparts.  This Amendment may be executed in counterparts, and all parties need not execute the same counterpart; however, no party shall be bound by this Amendment until the Credit Parties, the Agent and the Additional Revolving Lender have executed a counterpart.  Facsimiles or other electronic transmission (e.g., pdf) will be effective as originals.

5.5.          Complete Agreement.  THIS AMENDMENT, THE CREDIT AGREEMENT AND THE OTHER LOAN DOCUMENTS REPRESENT THE FINAL AGREEMENT AMONG THE PARTIES AND MAY NOT BE CONTRADICTED BY EVIDENCE OF PRIOR, CONTEMPORANEOUS OR ORAL AGREEMENTS OF THE PARTIES.  THERE ARE NO UNWRITTEN ORAL AGREEMENTS AMONG THE PARTIES.

5.6.          Headings.  The headings, captions, and arrangements used in this Amendment are, unless specified otherwise, for convenience only and will not be deemed to limit, amplify, or modify the terms of this Amendment, nor affect the meaning thereof.

[Signature Pages Follow]

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IN WITNESS WHEREOF, the parties hereto have caused this Amendment to be duly executed by their respective authorized officers on the date first written above.

[Signature Page]

JOINDER AND FOURTH AMENDMENT TO CREDIT AGREEMENT

SILVERTHORNE OPERATING LLC

[Signature Page]

JOINDER AND FOURTH AMENDMENT TO CREDIT AGREEMENT

SILVERTHORNE OPERATING LLC

[Signature Page]

JOINDER AND FOURTH AMENDMENT TO CREDIT AGREEMENT

SILVERTHORNE OPERATING LLC

[Signature Page]

JOINDER AND FOURTH AMENDMENT TO CREDIT AGREEMENT

SILVERTHORNE OPERATING LLC

SCHEDULE 1.1A

REVOLVING CREDIT COMMITMENTS

Schedule 1.1A-1