Oil prices extended gains on Friday and headed for a second weekly gain, supported by geopolitical tensions in Europe and the Middle East, concerns over tightening supply, and optimism about global fuel demand growth as economies improve. Brent crude climbed 49 cents, or 0.5%, to $91.14 a barrel. U.S. West Texas Intermediate crude was at $86.96 a barrel, up 37 cents, or 0.4%. Both benchmarks settled at their highest since October on Thursday. Brent and WTI are set to notch a more than 4% gain this week, climbing for a second straight week, after third-largest OPEC producer Iran vowed revenge against Israel for an attack that killed high-ranking Iranian military personnel. Israel has not claimed responsibility for the attack on Iran's embassy compound in Syria on Monday. Ongoing Ukrainian drone attacks on refineries in Russia may have disrupted more than 15% of Russian capacity, a NATO official said on Thursday, hitting the country's fuel output. The Organization of the Petroleum Exporting Countries (OPEC) and allies led by Russia, known as OPEC+, this week kept their oil supply policy unchanged and pressed some countries to increase compliance with output cuts. Investors are awaiting a U.S. March employment report later on Friday for further clues on the health of the U.S. economy and the direction of its monetary policy.