Crude oil prices were heading for weekly 3% gain for the week ending Oct. 11 amid OPEC's consideration of greater supply cuts to push prices higher.
An attack on an Iranian tanker also intensified worries of secure oil supply from the Middle East and supported higher prices.
International benchmark Brent crude was trading at $59.81 per barrel at 1300 GMT on Friday for a weekly gain of 3% after it started Monday at $58.02 a barrel.
American benchmark West Texas Intermediate was at $54.08 a barrel at the same time, heading for a 2.6% gain for the week, after opening Monday at $52.69 per barrel.
OPEC Secretary General Mohammed Barkindo said Thursday that the organization and its allies, dubbed as OPEC+, are contemplating deeper oil production cuts before their semi-annual meeting in Vienna on Dec. 5-6.
'All options are open,' Barkindo told reporters at an energy conference in London, adding that OPEC+ would take 'appropriate, strong, positive' decisions in the December meeting to sustain oil prices.
'The narrative continues to be gloomy,' he said regarding the global economy and the negative impact of the ongoing trade war between the U.S. and China.
OPEC lowered its global economic growth forecast for 2020 to 3% from its previous estimate of 3.1%, according to its Monthly Oil Market Report released on Thursday.
'... it seems increasingly likely that the slowing growth momentum in the U.S. will carry over into 2020, while ongoing uncertainties surrounding the EU, including Brexit, will remain,' the report said.
'Moreover, rising U.S. tariffs on EU imports and ongoing U.S.-China trade issues are dampening growth momentum,' it added.
- Invitation to U.S.
Barkindo reiterated his formal invitation to the U.S. to join the cooperation agreement between the 14 OPEC members and 10 non-OPEC oil producing nations including Russia.
'OPEC+ charter fits the U.S. very well. It's for all producers today and U.S. is the biggest producer,' he said.
Barkindo, however, told Russian news agency TASS on Monday that it is too early for OPEC+ to consider deepening cuts at its meeting in December, saying discussions over possible output cuts would be 'premature at the moment.'
OPEC+ had agreed on Dec. 7, 2018 to lower their total production level by 1.2 million barrels per day, and decided in early July this year to extend the agreement until the end of March 2020.
- Tanker attack
Crude prices also gained Friday after an Iranian tanker was reportedly hit off the coast of the Saudi Arabian city of Jeddah.
An oil spill occurred following the explosion that damaged the Iranian tanker in the Red Sea, according to Iranian state-run news agency IRNA.
National Iranian Tanker Company (NITC) said Friday in a statement that the hull of the tanker sustained two separate explosions 'probably caused by missile strikes.'
The NITC confirmed that the tanker is stable and all crew members are safe.
By Ovunc Kutlu