Filed Pursuant to Rule 424(b)(3)

Registration No. 333-217168

PROSPECTUS SUPPLEMENT NO. 4

(to Prospectus dated March 23, 2018)

169,933,626 Shares

GASTAR EXPLORATION INC.

Common Stock

This prospectus supplement is being filed to update and supplement information contained in the prospectus dated March 23, 2018, relating to the resale or other disposition of our common stock par value $0.001 per share, which may be offered for sale from time to time by the selling stockholders named in the prospectus, with information contained in our Current Report on Form 8-K, filed with the Securities and Exchange Commission on April June 11, 2018.

This prospectus supplement updates and supplements the information in the prospectus and is not complete without, and may not be delivered or utilized except in combination with, the prospectus, including any amendments or supplements thereto. This prospectus supplement should be read in conjunction with the prospectus and if there is any inconsistency between the information in the prospectus and this prospectus supplement, you should rely on the information in this prospectus supplement.

Investing in our securities involves risk. Please see “Risk Factors” beginning on page 3 of the prospectus for a discussion of certain risks that you should consider in connection with an investment in the securities.

Neither the Securities and Exchange Commission nor any state securities commission has approved or disapproved of these securities or determined if this prospectus is truthful or complete. Any representation to the contrary is a criminal offense.

This prospectus supplement is dated June 11, 2018.

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):  June 11, 2018

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 (see General Instruction A.2. below):

Indicate by check mark whether the registrant is an emerging growth company as defined in Rule 405 of the Securities Act of 1933 (§ 230.405 of this chapter) or Rule 12b-2 of the Securities Exchange Act of 1934 (§ 240.12b-2 of this chapter).

Emerging growth company ☐ If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 13(a) of the Exchange Act. ☐

SECTION 7 – REGULATION FD

Item 7.01 Regulation FD Disclosure.

On June 11, 2018, Gastar Exploration Inc. (“Gastar” or the “Company”) issued a press release announcing that it has declared a cash dividend on its 8.625% Series A Preferred Stock (“Series A Preferred Stock”) and its 10.75% Series B Preferred Stock (“Series B Preferred Stock”) for June 2018 and that it has elected to suspend the declaration and payment of monthly cash dividends on its Series A Preferred Stock and its Series B Preferred Stock commencing July 2018 to maintain liquidity to support its capital investment program.  A copy of the Company’s press release, dated June 11, 2018, is furnished herewith as Exhibit 99.1 and is incorporated herein by reference.  

In accordance with General Instruction B.2 of Form 8-K, the information presented herein under Item 7.01 and set forth in the attached press release included as Exhibit 99.1 to this report is deemed to be “furnished” solely pursuant to Item 7.01 of this report and shall not be deemed to be “filed” for purposes of Section 18 of the Securities Exchange Act of 1934, as amended (the “Exchange Act”), or otherwise subject to the liabilities of that section, nor shall such information or the exhibit be deemed incorporated by reference into any filing under the Securities Act of 1933, as amended, or the Exchange Act.

SECTION 8 - OTHER EVENTS

Item 8.01 Other Items.

On June 11, 2018, the Company announced that it has declared a cash dividend on its Series A Preferred Stock and its Series B Preferred Stock for June 2018 and that it has elected to suspend the declaration and payment of monthly cash dividends on its Series A Preferred Stock and its Series B Preferred Stock commencing July 2018 to maintain liquidity to support its capital investment program.  

SECTION 9 – FINANCIAL STATEMENTS AND EXHIBITS