Tesoro Corp., operator of the largest refinery in Hawaii, said today that third-quarter earnings fell from the same period a year ago on supply and production disruptions in California.

Tesoro reported net income of $283 million, or $1.92 a share, down from $345 million, or $2.39 a share, a year ago. Third-quarter revenue was $8.78 billion, up from $8.1 billion in the same period of 2011.

The company’s refining margin last quarter at its Campbell Industrial Park facility in Kapolei fell to $9.92 a barrel from $13.58 a barrel a year ago. The refining margin is the spread between the cost of crude oil and price of refined products. The Hawaii facility’s yield, or the total number of barrels of refined products of gas, jet fuel, diesel fuel and heavy oils, rose to 80,000 barrels a day from 76,000 barrels a day a year earlier.

San Antonio-based Tesoro in January said it was seeking a buyer for its Campbell Industrial Park refinery and chain of 31 Hawaii gas stations up for sale and that it expected to complete the sale no later than the end of this year.