Of the 48 exploration and production companies that applied for those drilling permits, Pioneer Natural Resources of Irving led with 19 applications for projects targeting the Spraberry field in Irion, Martin and Upton counties. Following Pioneer were XTO Energy, an Exxon Mobil subsidiary, with 17 drilling permit filings, Canadian oil company Encana with 12 applications and Midland exploration and production company Endeavor Energy Resources with 11.
