(past and present)
- Apache
- Black Arrow Energy
- Cimarex
- Devon
- Dwight Ross
- Enervest
- Jefferies Capital
- Jetta Operating
- Kinder Morgan
- Linn Energy
- Magnum Hunter Resources
- MacQuarie Capital
- Merlon International
- Midstates Petroleum
- Noble
- Penn Virginia
- Pitts Energy
- POG Resources
- Sterling Energy
- Tier Hydrocarbons
- Trincan Ltd.
- Tristone Capital
- Vess Oil
- Whiting Oil