Oil prices fell on Monday after U.S. drilling activity rose and fears waned about escalating tensions in the Middle East following air strikes on Syria over the weekend.
The United States, France and Britain launched 105 missiles on Saturday, targeting what they said were three chemical weapons facilities in Syria in retaliation for a suspected poison gas attack on April 7.
The oil price had risen nearly 10 percent in the run-up to the strikes, as investors bulked up on assets, such as gold or U.S. Treasuries, that can shield against geopolitical risks.
U.S. West Texas Intermediate crude futures ended Monday's session down $1.17, or 1.7 percent, at $66.22 a barrel. They hit a more than three-year closing high of $67.39 on Friday.
Brent crude oil futures were down $1.13, or 1.6 at $71.45 a barrel by 2:26 p.m. ET (1826 GMT). The contract toughed a high last week of $73.09 going back to November, 2014.