X0306 4 2018-02-01 0 0000086264 Carbon Natural Gas Co CRBO 0001667954 Yorktown Energy Partners XI, L.P. C/O YORKTOWN PARTNERS LLC 410 PARK AVENUE, 19TH FLOOR NEW YORK NY 10022 0 0 1 0 Common stock, par value $0.01 per share 2018-02-01 4 M 0 1527778 A 1527778 D Warrant 2018-02-01 4 M 0 1527778 D 2017-02-15 2024-02-15 Common Stock, par value $0.01 per share 1527778 0 D Series B Convertible Preferred Stock, par value $0.01 2018-04-06 4 P 0 50000 100.00 A 2018-04-06 Common Stock, par value $0.01 per share 50000 50000 D Shares received upon exercise of Warrant No. 1, issued on February 15, 2017 (the "Warrant") to the reporting person. The consideration the reporting person paid for the full exercise of the Warrant was the transfer and assignment to Carbon Natural Gas Company (the "Issuer") of 11,000 Class A Units of Carbon California Company, LLC, a Delaware limited liability company. On March 15, 2017, the Issuer effected a one for twenty reverse stock split of the Issuer's issued and outstanding common stock, as reported on the Current Report on Form 8-K filed by the Issuer with the SEC on March 16, 2017. As a result, the number of shares of common stock underlying the Warrant was proportionately reduced from 30,555,556 to 1,527,778. The Series B Convertible Preferred Stock converts into shares of the Issuer's common stock at the election of the holder and will automatically convert into shares of the Issuer's common stock if and when the Issuer completes a qualifying equity financing. The number of shares of common stock issuable upon conversion is dependent upon the price per share of common stock issued in connection with any such qualifying equity financing, but has an initial floor conversion price equal to $8.00 per share. The conversion price will be proportionately increased or decreased to reflect changes to the outstanding shares of common stock, such as the result of a combination, reclassification, subdivision, stock split, stock dividend or other similar transaction involving the common stock. The Series B Convertible Preferred Stock has no expiration date. However, it converts into shares of the Issuer's common stock at the election of the holder and will automatically convert into shares of the Issuer's common stock if and when the Issuer completes a qualifying equity financing. Yorktown Energy Partners XI, L.P., By: Yorktown XI Company LP, its general partner, By: Yorktown XI Associates LLC, its general partner, /s/ Peter A. Leidel, Manager 2018-04-09