Oil prices fell on Monday as a stronger dollar and ample U.S. supplies outweighed OPEC output curbs and rising tensions between the United States and Iran.
The Brent premium over WTI narrowed to about $2.15, its lowest since Feb. 1. If it stays at that level at the close, it would be the smallest premium since Jan. 16.
The dollar edged up versus a basket of currencies amid concerns over political uncertainty in Europe ahead of elections.
"It's most likely the stronger U.S. dollar," said Commerzbank analyst Carsten Fritsch of the reason for the dip in oil. A stronger dollar makes crude more expensive for other currency holders and usually weighs on the oil market.