Oil refiner Tesoro Corp. was stung by a $45 million net loss in the second quarter as a weak economy took its toll on sales and profit margins.

Tesoro, which operates one of two Hawai'i refineries and six other Western petroleum processing plants, also reported lower production compared to the April-to-June period last year, when it had a profit of $4 million.

Tesoro and other refiners have anticipated a tough year because of the economic slowdown. The company earlier this year said it was going to run its refineries at conservative levels because they expected lower demand, especially for diesel and distillate products.

"As we began 2009, we were prepared for a very difficult year, and in the second quarter it arrived," said Bruce Smith, chairman, president and chief executive officer of San Antonio-based Tesoro.

Revenues fell by more than half, to $4.18 billion from $8.89 billion a year earlier when gasoline prices headed for an all-time high.

Tesoro released operating data for its refineries that showed its Hawai'i refining operation ran at about 70 percent of capacity during the second quarter.

The company reported total production amounted to 66,000 barrels a day at the Kapolei facility, or 28,000 barrels lower than its 94,000 barrel-a-day capacity.

The refinery's average gasoline production was the same as a year earlier at 16,000 barrels daily, but production of jet fuel, diesel fuel and heavy oils and residual products were down compared to a year earlier.

Still, Tesoro reported a $2.52 gross refining margin per throughput barrel, or revenue, minus costs that include crude oil, transportation and distribution.

A year earlier the company had a negative $6.33 gross refining margin per throughput barrel. Tesoro does not break out separately financial data for its more than 30 retail service stations in the state.

Tesoro's operating data also shows Hawai'i's margin was the lowest of all its refineries but had the biggest improvement over the past year.

Tesoro's overall financial performance was mixed compared to estimates of financial analysts surveyed by Bloomberg L.P. While sales and net losses were worse than had been estimated, the refiner beat expectations for a loss adjusted for one-time gains and losses.

On this basis, Tesoro reported a loss of 24 cents a share. The average analyst estimate had been for a loss of 40.5 cents.

Tesoro reported its results after regular markets closed, during which its shares fell 2 cents to $13.07.

In after-hours trading the stock traded as high as $17.65.

Smith said the company continues to see difficult market conditions during the current quarter.