Brent crude was down $2.01, or 2.7%, at $71.58 a barrel by 0850 GMT. U.S. oil was down $2.06, or 2.8%, at $69.75 a barrel.
OPEC+ ministers agreed on Sunday to increase oil supply from August to cool prices that this month hit their highest level in more than two years as the global economy recovers from the COVID-19 pandemic.
The group of members of the Organization of the Petroleum Exporting Countries (OPEC) and allies such as Russia also agreed new production shares from May 2022.
OPEC+ last year cut output by a record 10 million barrels per day (bpd) amid an evaporation in demand the pandemic developed, prompting a collapse in prices with U.S. oil futures prices at one point falling into negative territory.
OPEC+ producers have gradually eased their output curbs, which now stand at around 5.8 million bpd.
"Even with higher output, the market remains relatively tight," ANZ Research said. "High frequency data is showing encouraging signs for oil, with U.S. gasoline demand recently hitting a record high. This should limit the duration of the selling."