JOINT FILERS’ SIGNATURES

R/C ENERGY IV DIRECT PARTNERSHIP, L.P.
By: Riverstone/Carlyle Energy Partners IV, L.P., its general partner
By:  R/C ENERGY GP IV, LLC, its general partner
By:	/s/ Peter Haskopoulos		Date: September 17, 2018
	Name:	Peter Haskopoulos
	Title:	Authorized Person
R/C IV LIBERTY HOLDINGS, L.P.
By:  Riverstone/Carlyle Energy Partners IV, L.P., its general partner
By:  R/C ENERGY GP IV, LLC, its general partner
By:	/s/ Peter Haskopoulos		Date: September 17, 2018
	Name:	Peter Haskopoulos
	Title:	Authorized Person
R/C ENERGY GP IV, LLC
By:	/s/ Peter Haskopoulos		Date: September 17, 2018
	Name:	Peter Haskopoulos
	Title:	Authorized Person