U.S. crude oil exports plunged by more than 40% in June, foreign trade data from the U.S. Census Bureau showed on Aug. 5, after Brent's premium to U.S. crude hovered in a tight band earlier this year.

Total exports dropped to 383,000 barrels per day (Mbbl/d) from May's record of 662 Mbbl/d, according to data compiled by Reuters.

Exports to Canada were 280 Mbbl/d vs. 308 Mbb/d one month prior. Exports to the U.K. were 37 Mbbl/d, nearly unchanged from May. Meanwhile, exports to Curacao were 17 Mbbl/d, a sharp drop from May's 67 Mbbl/d.

The export declines were likely a result of Brent's May and June contracts having traded in such a tight band to U.S. crude earlier this year. At one point, Brent even briefly traded at a discount. Typically, a wide premium for Brent over U.S. crude makes exports more economical.

The U.S. Census' foreign trade oil data is published weeks earlier than the closely-watched U.S. Energy Information Administration trade figures. The EIA, which bases its numbers on the census data, will release its monthly crude figures at the end of August.