EXHIBIT 1.1

JOINT FILING AGREEMENT

In accordance with Rule 13d-1(k) promulgated under the Securities Exchange Act of 1934, as amended, the undersigned persons hereby agree to the joint filing on behalf of each of them of a statement on Schedule 13D (including amendments thereto) with respect to the common stock, par value $0.01 per share of Carbon Natural Gas Company and further agree that this Joint Filing Agreement be included as an Exhibit to such joint filing. In evidence thereof each of the undersigned, being duly authorized, hereby execute this Agreement on the date set forth below.

Date: February 27, 2017

YORKTOWN ENERGY PARTNERS XI, L.P.

By:	Yorktown XI Company LP,
	Its General Partner
By:	Yorktown XI Associates LLC,
	Its General Partner
By:	/s/ Peter A. Leidel
	Name: Peter A. Leidel
	Title: Managing Member

YORKTOWN XI COMPANY LP

By:	Yorktown XI Associates LLC,
	Its General Partner
By:	/s/ Peter A. Leidel
	Name: Peter A. Leidel
	Title: Managing Member

YORKTOWN XI ASSOCIATES LLC

By:	/s/ Peter A. Leidel
	Name: Peter A. Leidel
	Title: Managing Member