 DENVER--BUSINESS WIRE--Liberty Oilfield Services Inc. NYSE: LBRT; Liberty or the Company announced today the appointment of Audrey Robertson to its Board of Directors. Ms. Robertson joined the Board contemporaneously with the resignation of Brett Staffieri, who previously served on the Board as a nominee of entities affiliated with Riverstone Holdings. Mr. Staffieri resigned after Riverstone completed the divestiture of its equity investment in the Company earlier this month. We are ex 