SINGAPORE: Oil prices fell by more than 1 percent on Monday as U.S. drilling activity picked up and as a refinery fire in the U.S. state of Illinois resulted in the shutdown of a large crude distillation unit.

U.S. West Texas Intermediate (WTI) crude futures were at $51.92 per barrel at 0144 GMT, down 80 cents, or 1.5 percent, from their last settlement.