On Thursday, US crude rose 4.5% to close at $40.20, after climbing as high as $40.26.

Brent crude's front-month contract was up 1 cent at $41.55. It finished up $1.21 at $41.54 a barrel on Thursday, after earlier reaching the year's peak of $41.60, a level that was matched earlier on Friday.

Oil prices have surged more than 50% from 12-year lows since Opec floated the idea of a production freeze, boosting Brent from about $27 a barrel and US crude from around $26.

US oil is heading for a fifth week of gains, the longest rising streak in about a year, while Brent is on course for a fourth weekly increase, the longest run in about 12 months.

But some are urging caution after the strong gains.

"Global fundamentals are little changed and oil has instead been lifted by higher risk-appetite," BNP Paribas said in a note.

"A dialogue among key producing countries to address oil output will at best yield a decision to freeze output, but not the much-needed reduction required to rebalance the market," BNP said.

BNP estimates there will be a 1 million barrel increase in global stocks by the end of the first half of 2016.

Still, a weakening dollar after a Federal Reserve policy decision on Wednesday that indicated two US rate hikes this year instead of four is also attracting oil buyers that hold other currencies.

Opec kingpin Saudi Arabia and non-Opec producers led by Russia will meet on 17 April in the Qatar capital Doha, aiming for the first global supply deal in 15 years.