Oil prices fell by about $3.5 a barrel in trading Tuesday, following reports British oil workers are back on the job after a two-day strike.

The strike shut down production at the Grangemouth refinery and forced the closure of a North Sea oil pipeline - which carries about 40 percent of Britain's oil - causing concerns about oil supplies.

Some economists say falling oil prices also are the result of the U.S. dollar, which has been strengthening against other currencies, including the euro.

Oil prices set a new record high Monday of almost $120 a barrel.

Meanwhile, oil giants Royal Dutch Shell and BP announced record profits for the first quarter of this year, driven by the overall higher price of crude oil.

Royal Dutch Shell says its first quarter net income jumped 25 percent to more than $9 billion. BP says its profits soared 63 percent to about $7.6 billion.

Both companies say oil and gas production remained unchanged during the quarter.

Investors still have some concerns about oil supplies, especially in Nigeria, where a strike by oil workers and violence have taken a toll on oil production. Royal Dutch Shell says militant attacks have forced it to suspend the production of about 164,000 barrels a day.

High oil prices are hurting some companies in the oil sector.

Valero, the largest oil refiner in the United States, blamed surging oil prices for a 77-percent drop in first-quarter earnings. The company says first-quarter income fell to $261 million.

Some information for this report was provided by AP.