NEW YORK (AP) -- Offshore drilling rig contractor Transocean Ltd. swung to a loss in the second-quarter despite higher revenue, as it set more money aside for losses related to the 2010 Gulf oil spill.

Its revenue topped expectations, and shares rose in trading Thursday before the opening bell.

The company reported a $304 million loss for the April-June period, which worked out to 86 cents per share. Transocean booked $1.58 per share in charges for the quarter, mostly due to $750 million in extra funds it set aside to prepare for settlements related to the Gulf oil spill.

Transocean, which is based in Zug, Switzerland, and has major operations in Houston, owned the Deepwater Horizon rig that caught fire and sank in the Gulf of Mexico in April 2010, leading to the worst offshore oil spill in U.S. history. Transocean in February estimated its losses at $1 billion from the spill.

In last year's second-quarter, it earned $124 million, or 39 cents per share. It adjusted its financial statements from last year to reflect insurance recoveries for legal and other costs from the spill.

The per-share results reflect a 10 percent increase in the number of outstanding shares since last year. The company issued more than 26 million shares in November, partly to raise money for an acquisition initially financed with debt.

Revenue in the second quarter rose 10 percent to $2.58 billion. It raked in more money from drilling as rigs spent more time offline and it squeezed more efficiency out of its operations.

Analysts, on average, expected a profit of 44 cents per share, on revenue of $2.5 billion, according to FactSet.

Transocean owns or has a stake in a fleet of 128 mobile offshore drilling units. Its stock closed Wednesday at $47.80. In premarket trading, shares gained 65 cents to $48.45.