According to this link, these energy companies are actively working in the Wolfcamp Shale (Wolfberry Trend): http://oilshalegas.com/wolfcampshale.html
Apache
Approach Resources
Chesapeake Energy
Cimarex Energy
Concho Resources
Conoco Phillips
Devon Energy
EOG Resources
Forest Oil
Linn Energy
Petrohawk Energy
Pioneer Natural Resources
Sandridge Energy
Southwestern Energy
Whiting Petroleum