UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 8-K

CURRENT REPORT

Pursuant to Section 13 or 15(d)

of the Securities Exchange Act of 1934

Date of Report (Date of earliest event reported): May 9, 2014

QUEST RESOURCE HOLDING CORPORATION

(Exact Name of Registrant as Specified in Charter)

Registrant’s telephone number, including area code: (972) 464-0004

Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions:

Item 1.01. Entry into a Material Definitive Agreement.

Reference is made to Item 2.03 of this Current Report on Form 8-K. The disclosure contained in Item 2.03 and the information contained in Exhibit 10.19(a) through Exhibit 10.19(c) attached hereto are hereby incorporated by reference in their entirety into this Item 1.01.

Item 2.03. Creation of a Direct Financial Obligation or an Obligation under an Off-Balance Sheet Arrangement of a Registrant.

Our indirect wholly owned subsidiary, Quest Resource Management Group, LLC (“Quest”), entered into a Sixth Amendment to Loan Agreement, dated as of May 9, 2014 (the “Amendment”), with Regions Bank (the “Lender”). Capitalized terms used herein have the meanings set forth in the Loan Agreement (as defined in the Amendment). The Amendment amended the Loan Agreement to, among other things, (i) add a $5.0 million accordion feature, (ii) increase the Borrowing Base, (iii) reduce the Applicable Margin for Eurodollar Rate Loans by 1% per annum, (iv) add an unused fee of 0.25% per annum, (v) extend the maturity date to May 31, 2015, (vi) release the Guaranty of Brian Dick previously executed in favor of the Lender, (vii) add our company and our wholly owned subsidiary, Earth911, Inc. (“Earth911”), as Guarantors, (viii) allow for Permitted Acquisitions, and (ix) delete two of the financial covenants and modify the other financial covenants in certain respects.

In connection with the Amendment, on May 9, 2014, we and Earth911entered into a Guaranty (the “Guaranty”) for the benefit of the Lender to guarantee the obligations of Quest under the Loan Agreement and other Loan Documents. In addition, on May 9, 2014, Earth911 entered into a Pledge Agreement (the “Pledge Agreement”) with the Lender, pursuant to which Earth911 pledged to the Lender 50% of the membership interests in Quest held by Earth911 to secure the prompt and complete payment and performance of the obligations of Quest and the Guarantors under the Loan Agreement and other Loan Documents.

The foregoing description of the Amendment, the Guaranty, and the Pledge Agreement are summaries only and are qualified in their entirety by reference to the full text of the Amendment, the Guaranty, and the Pledge Agreement, which are attached hereto as Exhibit 10.19(a), Exhibit 10.19(b), and Exhibit 10.19(c), respectively.

Item 9.01. Financial Statements and Exhibits.

Not applicable.

Not applicable.

Not applicable.

SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned hereunto duly authorized.

EXHIBIT INDEX