Oil prices fell on Wednesday on expectations increased exports from Iran will add to a global supply glut and on rising inventories at the delivery hub at Cushing, Oklahoma.
Tuesday's agreement on Tehran's nuclear program between six world powers and Iran is expected to result in the lifting of sanctions in early 2016 which have limited sales of Iranian oil for several years.
U.S. crude closed down $1.63, or 3.1 percent, at $51.41 a barrel. That was the lowest settlement since April 9. Brent crude was down $1.40 at $57.10 a barrel, having swung from $57.29 to $58.81. The August contract expires on Thursday.
Oil prices slumped even though U.S. crude stocks fell 4.3 million barrels last week, according to the Energy Information Administration (EIA), as refiners boosted throughput to a record level.
While the inventory slide was more than analysts' expectations for a decrease of 1.2 million barrels, the drop was less than the 7.3 million-barrel decline reported on Tuesday by the industry group American Petroleum Institute (API).