Shares of Hawai'i's biggest refiner, Tesoro Corp., have soared nearly 50 percent since the beginning of this year to just under $100 a share, bucking a trend of declining stock prices at other oil companies.

Oil company profits have been a source of controversy for years in large part because of high gasoline prices. However, the recent spike in San Antonio, Texas-based Tesoro's stock is largely the result of the company's announcement that it is acquiring a refinery and nearly 400 gas stations in California, according to analysts.

Shares of Tesoro rose 22 cents to $97.76 yesterday on the New York stock Exchange. That's up 47 percent since the start of the year. At the same time, shares of Hawai'i's other refiner, Chevron Corp., have fallen 6 percent to close yesterday at $68.87.

Much of the gain in Tesoro shares came following the company's Jan. 29 announcement that it planned to buy Royal Dutch Shell Plc's plant near Los Angeles along with 250 Southern California gasoline stations for $1.63 billion.

"Since then, it's been on a tear mostly because of that deal," said Jim Byrne, an analyst with BMO Capital Markets in Toronto, Canada. "It forced people to revise they're earnings estimates higher."

On that same day, Tesoro also announced an agreement to buy 140 USA Petroleum gasoline stations mostly in California and a New Mexico fuel terminal for $277 million.

The stock received a further boost on a recent spike in California gasoline prices on supply concerns. The average price for regular in California has risen nearly 48 cents a gallon in the last month to $3.121, according to the AAA Daily Fuel Gauge Report.

Tesoro "is the biggest West Coast refiner and margins are the biggest on the West Coast," Byrne added.

Bruce Smith, Tesoro's chief executive, told Bloomberg News that the Shell acquisition would pay for itself within four years.

Smith also speculated that crude oil prices will remain in the $60-a-barrel range this year.

"Cheap gas ain't gonna happen," Smith told Bloomberg News in a March 2 story. "I used to say it was going to be over in 2010-2012. I think it's going to go on for a long time now."

Reach Sean Hao at shao@honoluluadvertiser.com.