SEC Form 4

FORM 4		UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 STATEMENT OF CHANGES IN BENEFICIAL OWNERSHIP Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934 or Section 30(h) of the Investment Company Act of 1940	OMB APPROVAL OMB Number: 3235-0287 Estimated average burden hours per response: 0.5
	Check this box if no longer subject to Section 16. Form 4 or Form 5 obligations may continue. See Instruction 1(b).

1. Name and Address of Reporting Person* Yorktown XI Associates LLC (Last) (First) (Middle) C/O YORKTOWN PARTNERS LLC 410 PARK AVENUE, 19TH FLOOR (Street) NEW YORK NY 10022 (City) (State) (Zip)	2. Issuer Name and Ticker or Trading Symbol Carbon Natural Gas Co [ CRBO ]	5. Relationship of Reporting Person(s) to Issuer (Check all applicable) Director X 10% Owner Officer (give title below) Other (specify below)
	3. Date of Earliest Transaction (Month/Day/Year) 02/01/2018
	4. If Amendment, Date of Original Filed (Month/Day/Year)	6. Individual or Joint/Group Filing (Check Applicable Line) X Form filed by One Reporting Person Form filed by More than One Reporting Person

Table I - Non-Derivative Securities Acquired, Disposed of, or Beneficially Owned
1. Title of Security (Instr. 3)	2. Transaction Date (Month/Day/Year)	2A. Deemed Execution Date, if any (Month/Day/Year)	3. Transaction Code (Instr. 8)		4. Securities Acquired (A) or Disposed Of (D) (Instr. 3, 4 and 5)			5. Amount of Securities Beneficially Owned Following Reported Transaction(s) (Instr. 3 and 4)	6. Ownership Form: Direct (D) or Indirect (I) (Instr. 4)	7. Nature of Indirect Beneficial Ownership (Instr. 4)
			Code	V	Amount	(A) or (D)	Price
Common stock, par value $0.01 per share	02/01/2018		M		1,527,778(1)	A	(2)	1,527,778	I	See Footnotes(3)(4)

Table II - Derivative Securities Acquired, Disposed of, or Beneficially Owned (e.g., puts, calls, warrants, options, convertible securities)
1. Title of Derivative Security (Instr. 3)	2. Conversion or Exercise Price of Derivative Security	3. Transaction Date (Month/Day/Year)	3A. Deemed Execution Date, if any (Month/Day/Year)	4. Transaction Code (Instr. 8)		5. Number of Derivative Securities Acquired (A) or Disposed of (D) (Instr. 3, 4 and 5)		6. Date Exercisable and Expiration Date (Month/Day/Year)		7. Title and Amount of Securities Underlying Derivative Security (Instr. 3 and 4)		8. Price of Derivative Security (Instr. 5)	9. Number of derivative Securities Beneficially Owned Following Reported Transaction(s) (Instr. 4)	10. Ownership Form: Direct (D) or Indirect (I) (Instr. 4)	11. Nature of Indirect Beneficial Ownership (Instr. 4)
				Code	V	(A)	(D)	Date Exercisable	Expiration Date	Title	Amount or Number of Shares
Warrant	(2)	02/01/2018		M			1,527,778(5)	02/15/2017	02/15/2024	Common Stock, par value $0.01 per share	1,527,778(5)	(2)	0	I	See Footnotes(3)(4)
Series B Convertible Preferred Stock, par value $0.01	(6)	04/06/2018		P		50,000		04/06/2018	(7)	Common Stock, par value $0.01 per share	50,000	$100	50,000	I	See Footnotes(3)(4)

Explanation of Responses:

1. Shares received upon exercise of Warrant No. 1, issued on February 15, 2017 (the "Warrant") to Yorktown Energy Partners XI, L.P. ("Yorktown XI").

2. The consideration Yorktown XI 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.

3. These securities are directly owned by Yorktown XI. The reporting person is the sole general partner of Yorktown XI Company LP, the sole general partner of Yorktown XI.

4. The reporting person disclaims beneficial ownership of these securities except to the extent of its pecuniary interest therein, and this report shall not be deemed an admission that the reporting person is the beneficial owner of the securities for Section 16 or any other purpose.

5. 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.

6. 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.

7. 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.

Remarks:

	Yorktown XI Associates LLC, /s/ Peter A. Leidel, Manager	04/09/2018
	** Signature of Reporting Person	Date
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