Fellow workers searched into the evening Saturday for an employee missing after an explosion and fire at the Marathon Petroleum Co. refinery in St. Paul Park.

The fire was reported about 8:30 a.m. and was declared out within an hour, Washington County authorities said.

An employee working among the big tanks was still missing late Saturday, said Bob Behr, the refinery's human resources manager. No workers were reported injured.

"We are very concerned and will keep looking until we find him," Behr said of the missing man, whose name was not released. He said about a dozen employees searched the approximately 10-acre tank farm without finding any trace of the man, who Behr said had worked at least a few years for Marathon as an operator who moved oil products between tanks during the refining process.

The damage was confined to a relatively small 10,000-barrel tank that contained about 8,000 gallons of fuel oil when the fire broke out, Behr said.

It wasn't immediately clear whether production at the refinery would be affected, Behr said.

The cause was not known and there is no damage estimate yet, but there was no impact outside of the refinery, he said. He said workers heard a boom and then noticed the tank fire. Firefighters from St. Paul Park, Newport, Cottage Grove, Woodbury, Maplewood and Inver Grove Heights responded to the refinery southeast of St. Paul.

The refinery has a capacity of 70,000 barrels per day and processes almost entirely crude oil from Canada into gasoline, diesel, fuel oil, jet fuel, propane and asphalt. Most gasoline produced at the refinery is marketed at local stations.

According to the company's website, the plant has won several awards for workplace safety in recent years. Earlier this fall, however, an explosion injured three workers, one seriously. The cause of that blast remains under investigation.

Last week, an oil pipeline fire near Clearbrook in northern Minnesota killed two workers and briefly caused world oil prices to spike. The Enbridge Energy pipeline system in that area carries roughly 16 percent of U.S. crude imports.

The company said the system was soon running at 80 percent capacity on three of its four lines, and spokesman Larry Springer said Friday that the remaining line may be ready to carry oil again in the coming week.

The Associated Press contributed to this report. Jim Adams • 612-673-7658