PureWest Energy (formerly known as Ultra Petroleum) is an oil and gas company that engages in the acquisition, exploration, development, operation, and production of oil and natural gas properties. Its principal business activities are developing its natural gas reserves in the Green River Basin of southwest Wyoming, the Pinedale and Jonah fields; its oil reserves in the Uinta Basin in northeast Utah; and its natural gas reserves in the north-central Pennsylvania area of the Appalachian Basin.