Exhibit 5.1

1000 Main Street, 36^th Floor Houston, Texas 77002 Telephone {713} 226-6000 Telecopier {713} 228-1331 porterhedges.com

January 24, 2018

Synthesis Energy Systems, Inc.

Three Riverway, Suite 300

Houston, Texas 77056

Ladies and Gentlemen:

We have acted as special counsel to Synthesis Energy Systems, Inc., a Delaware corporation (the “Company”), in connection with the registration under the Securities Act of 1933, as amended (the “Securities Act”), on a registration statement on Form S-3, as may be amended from time to time (the “Registration Statement”), filed with the Securities and Exchange Commission (the “SEC”), for the offer and sale by the selling stockholders named in the Registration Statement, of up to 1,070,000 shares (the “Shares”) of the Company’s common stock, par value $0.01 per share.

As the basis for the opinions hereinafter expressed, we have examined: (i) originals, or copies certified or otherwise identified, of (a) the Registration Statement; (b) the Certificate of Incorporation of the Company, as amended to date; (c) the Amended and Restated Bylaws of the Company, as amended to date; (d) certain resolutions of the Board of Directors of the Company; and (e) such other instruments and documents as we have deemed necessary or advisable for the purposes of this opinion; and (ii) such statutes, including the General Corporation Law of the State of Delaware, and regulations as we have deemed necessary or advisable for the purposes of this opinion. We have not independently verified any factual matter relating to this opinion.

In making our examination, we have assumed and have not verified (i) that all signatures on documents examined by us are genuine, (ii) the legal capacity of all natural persons, (iii) the authenticity of all documents submitted to us as originals and (iv) the conformity to the original documents of all documents submitted to us as copies thereof.

Based on the foregoing, and subject to the assumptions, exceptions and qualifications set forth herein, we are of the opinion that the Shares have been validly issued and are fully paid and non-assessable.

The opinions expressed herein are limited to the General Corporation Law of the State of Delaware and the federal securities laws of the United States of America.

We hereby consent to the filing of this opinion as an exhibit to the Registration Statement and to the reference to our firm under the caption “Legal Matters” in the prospectus included as a part of the Registration Statement. In giving this consent, we do not thereby admit that we are included in the category of persons whose consent is required under Section 7 of the Securities Act or the rules and regulations of the SEC issued thereunder.

Very truly yours,

/s/ Porter Hedges LLP

PORTER HEDGES LLP