West Texas Intermediate futures for August delivery fell to $51.70 (-1.20%); Brent crude declined to $56.23 (-1.09%) as concerns over Greece and selloff in Chinese stocks outweighed expectations for a further drop in U.S. crude oil inventories. The American Petroleum Institute (API) estimated an almost 960,000-barrel drop. Government data will be published this afternoon.

Meanwhile the U.S. Energy Information Administration reported Tuesday that U.S. production fell from a 44-year high in May and is expected to keep declining through February 2016. Despite declines in U.S. output the agency expects global supplies to exceed consumption in 2015 and 2016.

The deadline for a deal between Iran and global powers was extended to July 10. Expectations for more supplies from OPEC's fifth-largest producer weigh on crude prices.