US crude was down 85 cents at $40.23. The contract rose $1.30, or 3.3%, to $41.08 in the previous session.

Kuwaiti oil and gas workers ended a three-day strike that had temporarily cut the Opec member's crude production by nearly half, the trade union said in a statement posted on its Twitter account on Tuesday.

Kuwait Oil Company was forced to cut output to as little as 1.1 million barrels per day from a normal level of about 3 million bpd. By Tuesday, output had recovered to around 1.5 million bpd.

The end of the strike revived the bearish mood brought on by the failure of major producers to reach an agreement on Sunday on a production freeze, to help overcome a market imbalance that has caused a slump in prices since 2014.

"In the near term we are going to see more downward pressure than upward," said IHS analyst Victor Shum.

Adding to the bearish tone, data from industry group American Petroleum Institute (API) also showed US crude stocks rose more than anticipated last week.

Crude inventories rose by 3.1 million barrels in the week to 15 April to 539.5 million, compared with analysts' expectations for a rise of 2.4 million barrels. Crude stocks at the Cushing, Oklahoma, delivery hub fell by 235,000 barrels, API said.