U.S. oil refiners are set to dramatically increase fuel production over the next few weeks, easing a crunch in gasoline stockpiles in the midst of summer driving season.

The boost in refining activity would end a prolonged stretch of maintenance and unplanned outages that has plagued the industry since winter, cutting into refined fuel stocks and allowing raw crude inventories to climb to their highest level since 1998.

"We are going to see an increase in U.S. fuel output with refineries coming back online, and also an increase in oil demand for the same reason," said Jason Schenker, economist at Wachovia Bank.

U.S. oil prices jumped more than $1 on Friday as dealers anticipated the higher demand for crude from the nation's refineries, as well as peak demand for gasoline over the looming July 4 Independence Day holiday.

"We're heading into the July 4 holiday, the peak of summer demand, at the same time refineries are coming back on line. That's what's holding up this market," said Schenker.

At least a half dozen oil refineries were restarting major processing units from maintenance at the end of June into early July, representing more than 3 percent of U.S. refinery capacity, according to a Reuters survey.

The restarts come after months of unusually low production from the U.S. refining industry that sliced some 15 percent off gasoline stockpiles between February and May and contributed to a record spike at the pumps.

Energy analysts have said refiners have been having trouble producing high-quality fuels from their aging plants, and may also be facing problems scheduling contractors to do regular turnaround work.

"Our seasonal refinery patterns are changing. In the past, we may have seen peak refinery output in the lead-up to summer. Now we'll likely be seeing peak refinery activity during peak demand," said Tim Evans, energy analyst at Citigroup Global Markets.

Oil refineries were running at 89.4 percent of capacity in the week ended June 22, according to the latest government data, sharply below the normal range around 95 percent for this time of the year. But utilization rates could soon climb into the low to mid-90 percent range as refiners recover.

Among the biggest refinery restarts, Exxon Mobil (XOM) is planning to fully restart a 240,000-barrel-per-day crude oil processing unit at its refinery in Beaumont, Texas, by early July.

BP Plc is also in the process of restarting a 75,000 bpd crude unit at its refinery in Whiting, Indiana -- the fourth largest oil refinery in the United States -- a source familiar with the plant said.

The unit is one of two that has been shut at the plant since a fire in early April.