US crude oil futures were steady around $59.70 a barrel in quiet trade on Friday with many major markets closed for May Day, after posting the biggest monthly gain in six years in April.

US crude for June delivery was 4 cents higher at $59.67 a barrel by 1145 GMT. In April, the contract rose by a quarter, the best monthly gain since May 2009, and on Thursday touched a 2015-high of $59.85.

Brent crude futures, the more widely-used benchmark, was yet untraded after rising 21 per cent in April and reaching a high on Thursday for the year of $66.93 a barrel. The contract settled at $66.69.

OPEC oil supply in April has jumped to its highest in more than two years, boosted by record or near-record supplies from Iraq and Saudi Arabia, a Reuters survey showed, as key members stand firm in their focus on market share.

Saudi Arabian King Salman's appointment of two new heirs will help stabilise world oil markets by strengthening political stability in the kingdom, its Oil Minister Ali al-Naimi was quoted as saying by state media on Thursday.

Oil is likely to stay relatively weak for at least the next year, a Reuters poll forecast on Thursday, suggesting a slowdown in oil production in the United States will not be enough to offset a global supply glut.

Exxon Mobil Corp's first-quarter profit dropped less than expected in results posted on Thursday as margins at the refining unit of the world's largest publicly traded oil company surged on tumbling crude prices.

Refining and trading cushioned a drop in Royal Dutch Shell's first quarter profits, which fell less than expected after the collapse in oil prices slashed earnings from oil and gas output.

US stocks, led by the Nasdaq, sold off on Thursday as Apple shares declined, and tech and biotech quarterly results disappointed.

The dollar rose against the Japanese yen Thursday after US data showed signs of a stabilizing labour market and an economy that was gathering momentum, putting the Federal Reserve on track to raise interest rates at least once this year.