Oil prices reversed early gains to settle lower Monday, as concerns about rising U.S. crude output continued to weigh on the market.

Oil prices initially rebounded in the early trading Monday after the first round of the French presidential election eased fears that France might leave the European Union. However, they then turned lower on persisted U.S. oil production concerns.

In the week ended April 21, the number of rigs operating in U.S. fields increased by 5 to 688, marking a fourteenth straight weekly gains, according to data released by oilfield service company Baker Hughes on Friday.

U.S. crude production is at 9.3 million barrels per day, up almost 10 percent since mid-2016, according to the CNBC.

The West Texas Intermediate for June delivery decreased 0.39 U.S. dollar to settle at 49.23 dollars a barrel on the New York Mercantile Exchange, while Brent crude for June delivery dipped 0.36 dollar to close at 51.60 dollars a barrel on the London ICE Futures Exchange.