NEW YORK—Oil prices fell Friday as U.S. drilling activity picked up.

The number of rigs drilling for oil in the U.S. rose by nine this week, the first increase in 11 weeks, Baker Hughes Inc. said Friday.

The oil-rig count has plunged to multiyear lows in recent months as more than a year of low oil prices has prompted companies to sharply cut spending on new drilling. But oil prices have climbed more than 80% since February, fueling expectations that some companies would decide to start drilling again and flood the still-oversupplied market with more crude.

“Any event that pumps up oil production and supplies once again will likely be oil-price negative,” John LaForge, head of real asset strategy at the Wells Fargo Investment Institute, said in a note. “By year-end 2016, we envision oil prices slipping back below $45 per barrel.”

Weaker-than-expected U.S. jobs data also weighed on oil prices Friday by lowering expectations for gasoline demand.