Patterson-UTI Energy ( PTEN - Get Report), a contract oil and natural gas driller, said its second-quarter earnings rose 131.9%, owing to higher prices of its rigs. The company earned $171.7 million, or $1 a share, in the quarter, compared with $74 million, or 43 cents a share, a year ago. Analysts surveyed by Thomson First Call were expecting earnings of 95 cents a share in the most recent quarter. Second-quarter revenue rose 63.3% from a year ago to $636.8 million, topping analysts' expectation of $607 million. The company also said that its board has authorised a buyback of up to $250 million of the company's stock. The company has already completed a buyback of $200 million, the Snyder, TX-based company said. "Demand for our drilling services continues to exceed the supply of available rigs. As a result, the pricing of our drilling rigs has continued to improve but the current gas storage overhang has moderated the rate of increase," the company said. The company's shares were down 94 cents, or 3.3%, at $27.29 in recent trading.