Tesoro Corp. swung to a $97 million profit from a year earlier loss during the fourth quarter, helped in part by a jump in profitability at its Hawai'i operations.

The San Antonio company reported the October-to-December period's profit compared with a $40 million loss a year earlier as it improved operations at its Hawai'i and California retail sites. Tesoro operates seven refineries, included one at Campbell Industrial Park that is the largest in the state.

"The actions we've been taking since late in 2007 have positioned the company to succeed even in this weak market environment," Bruce Smith, Tesoro chairman, said in a press statement.

The profit, adjusted for one-time items, was 99 cents a share, beating the 97 cents average forecast of 10 analysts surveyed by Bloomberg L.P.

Revenue for the quarter fell to $4.33 billion from $6.53 billion a year earlier.

Hawai'i operations played a large part in the profit increase, as the refinery here produced a $140 million gross refining margin compared with a $51 million loss last year. Tesoro has taken steps to modify the plant to handle heavier crude oil in addition to the light sweet crude from Asia, while getting better prices for its production.

Those changes helped the refinery transition from being Tesoro's worst to the best in terms of a closely watched industry metric, gross refining margin per throughput barrel.

Gross refining margin is revenue minus the cost of crude oil, purchased refined products, transportation and distribution.

In Hawai'i, the fourth-quarter margin per barrel was $23.42, compared with a negative $7.42 last year.

An analyst last month said he expected better Tesoro earnings to be led by improvements in the Hawai'i operations because earnings here benefit from falling crude prices and strong fuel oil markets.

For Tesoro as a whole, the gross refining margin per barrel was $12.47.

The company also said the total throughput of the Hawai'i refinery was 66,000 barrels a day, as opposed to 74,000 last year. It said its manufacturing costs here were higher here because of the price energy it bought.

Overall profitability of the company was also helped by improved retail results.