Solaris Energy Infrastructure (SEI) SC 13G Solaris Oilfield Infrastructure, Inc.

Exhibit 1.1

JOINT FILING AGREEMENT

In accordance withRule 13d-1(k)(1) under the Securities Exchange Act of 1934, as amended, the persons named below agree to the joint filing on behalf of each of them of a statement on Schedule 13G (including amendments thereto) with respect to the Class A common stock, par value $0.01 per share of SOLARIS OILFIELD INFRASTRUCTURE, INC., a Delaware corporation, and further agree that this Joint Filing Agreement be included as an exhibit to such joint filings. In evidence thereof, each of the undersigned hereby executes this Joint Filing Agreement as of February 14, 2018.

Yorktown Energy Partners X, L.P.
By:	Yorktown X Company LP,
	Its general partner
By:	Yorktown X Associates LLC,
	Its general partner
By:	/s/ Robert A. Signorino
Name:	Robert A. Signorino
Title:	Manager
Yorktown X Company LP
By:	Yorktown X Associates LLC,
	Its general partner
By:	/s/ Robert A. Signorino
Name:	Robert A. Signorino
Title:	Manager
Yorktown X Associates LLC
By:	/s/ Robert A. Signorino
Name:	Robert A. Signorino
Title:	Manager