Oil prices on Tuesday were holding just below four-year highs hit in the previous session, as looming U.S. sanctions against Iran and unwillingness by the Organization of the Petroleum Exporting Countries (OPEC) to raise output supported the market.
Brent crude futures LCOc1 were at $81.39 per barrel at 0535 GMT, up 19 cents, or 0.2 percent, and close to the intraday peak touched the previous day at $81.48, the highest level since November 2014, Reuters said.
U.S. West Texas Intermediate (WTI) crude futures CLc1 were at $72.18 a barrel, up 10 cents, or 0.1 percent from their last settlement.
The United States from November 4 will target Iran's oil exports with sanctions, and Washington is putting pressure on governments and companies around the world to fall in line and cut purchases from Tehran.
"Iran will lose sizeable export volumes, and given OPEC+ reluctance to raise output, the market is ill-equipped to fill the supply gap," Harry Tchilinguirian, global head of commodity markets strategy at French bank BNP Paribas, told the Reuters Global Oil Forum on Tuesday.
OPEC+ is the name given to the group of oil producers, including non-OPEC supplier Russia, that agreed to curtail output starting in 2017.
While Britain, China, France, Germany, Russia and Iran on Tuesday said they were determined to develop payment mechanisms to continue trading despite the sanctions by the United States, most analysts expect Washington's actions to knock between 1 million and 1.5 million barrels per day (bpd) of crude oil supplies out of markets.