Brent crude was up 62 cents, or 1.2 percent, at $51.17 a barrel by 9:01 a.m. ET (1301 GMT), having hit an intraday peak of $51.30 earlier in the day, their highest since October.
U.S. crude rose 61 cents to $50.30 a barrel, having touched a fresh 2016 peak of $50.37, their highest since October last year.
"With Brent staying above $50, oil is on an upward momentum with the restart of French refineries that were shut on strikes and pipeline attacks in Nigeria," said Kaname Gokon at brokerage Okato Shoji in Tokyo.
Preliminary work got underway on Monday to restart three of Total's French oil refineries, stopped as part of nationwide strikes, which would lead to higher crude demand.
Crude futures have gained more than 85 percent from this year's lows following supply outages in Canada, Venezuela, Libya and Nigeria.
Nigeria's Bonny Light crude output is down by an estimated 170,000 barrels per day (bpd) following attacks on pipeline infrastructure, according to a source.
While OPEC failed to agree on a clear oil-output strategy last week, traders said Saudi Arabia's promise not to flood the market has provided support to oil.
Oil was also propped up by a weak dollar, which wallowed near four-week lows against a basket of currencies. Federal Reserve Chair Janet Yellen said interest rate hikes are coming but gave little sense of when.
U.S. commercial crude oil inventories likely fell by 3.5 million barrels last week, marking a third straight weekly drop, a preliminary Reuters poll showed ahead of the data by the American Petroleum Institute due out at 4:30 p.m. ET (2030 GMT).
Oil also got support after market intelligence firm Genscape reported a drawdown of 1.08 million barrels at the Cushing, Oklahoma delivery point for WTI futures last week.
But this support may prove fleeting.
The market is braced for signs of recovering U.S. oil production after weekly data from Baker Hughes showed that U.S. drillers added rigs for only the second time this year, analysts said.
"Oil prices at $50 a barrel could revive shale drilling activity and stabilize declining U.S. oil production, possibly already harbingered by the recent uptick in rig counts," said Norbert Rücker, head of commodities research