X0206 3 2014-08-14 0 0000086264 Carbon Natural Gas Co CRBO 0001044321 MARXE AUSTIN W & GREENHOUSE DAVID M C/O SPECIAL SITUATIONS FUNDS 527 MADISON AVENUE, SUITE 2600 NEW YORK NY 10022 0 0 1 0 Common Stock 10888889 I By Limited Partnerships This is a joint filing by Austin W. Marxe (Marxe), David M. Greenhouse (Greenhouse) and Adam C. Stettner (Stettner). They share voting and investment control over all securities owned by Special Situations Fund III QP, L.P. (QP), Special Situations Cayman Fund, L.P. (Cayman) and Special Situations Private Equity Fund, L.P. (PE), respectively. 7,555,556 shares of Common Stock are held by QP, 2,222,222 shares of Common Stock are held by Cayman and 1,111,111 shares of Common Stock are held by PE. The interest of Marxe, Greenhouse and Stettner in the shares of Common Stock owned by QP, Cayman and PE is limited to the extent of his pecuniary interest. Pursuant to a Stock Purchase Agreement the Issuer re-purchased shares of its common stock. As a result, the total percentage of ownership owned by the Funds named in footnote 1 has increased to greater than 10%. Austin W. Marxe 2014-11-10 David M. Greenhouse 2014-11-10 Adam C. Stettner 2014-11-10