X0206 3 2015-01-29 0 0000086264 Carbon Natural Gas Co CRBO 0001535264 AWM Investment Company, Inc. 527 MADISON AVENUE SUITE 2600 NEW YORK NY 10022 0 0 1 0 Common Stock 10888889 I By Limited Partnerships AWM Investment Company, Inc., a Delaware corporation (AWM), is the investment adviser to Special Situations Fund III QP, L.P. (SSFQP), Special Situations Cayman Fund, L.P. (CAYMAN) and Special Situations Private Equity Fund, L.P. (SSPE and together with SSFQP and CAYMAN, the Funds). As the investment adviser to the Funds, AWM holds sole voting and investment power over. 7,555,556 shares of Common Stock of the Issuer (the Shares) held by SSFQP, 2,222,222 Shares held by CAYMAN and 1,111,111 Shares held by SSPE. Austin W. Marxe (Marxe), David M. Greenhouse (Greenhouse) and Adam C. Stettner (Stettner) are the controlling principals of AWM. Marxe, Greenhouse and Stettner previously reported the Shares held by the Funds on Form 3. Accordingly, reference should be made to Marxe, Greenhouse and Stettner (CIK #0001044321) for any prior filings with the Securities and Exchange Commission relating to the Shares held by each of the Funds. The reporting person disclaims beneficial ownership of the Shares, except to the extent of its pecuniary interest therein. This report shall not be deemed an admission that the reporting person is the beneficial owner of the securities reported herein for purposes of Section 16 of the Securities Exchange Act of 1934, as amended, or for any other purpose. Adam C. Stettner 2015-01-29