Oil rose by more than $1 a barrel to above $71 as hopes that the Omicron coronavirus variant may cause mostly mild symptoms boosted riskier assets and as the prospect of an imminent rise in Iranian oil exports looked less likely.
Helping ease Omicron concerns, reports in South Africa said cases there only had mild symptoms and the top U.S. infectious disease official told CNN "it does not look like there's a great degree of severity" so far.
Brent crude gained $1.77, or 2.5%, to $71.65 by 0920 GMT while U.S. West Texas Intermediate crude advanced $1.69, or 2.6%, to $67.95. Both benchmarks declined for a sixth week in a row last week.
The easing of Omicron fears also boosted European equities and safer havens like bonds gave up some recent gains.
Brent has risen 38% this year, supported by output curbs led by the Organization of the Petroleum Exporting Countries and allies, known as OPEC+, and recovering demand, although it has fallen from a three-year high above $86 in October.
OPEC+ decided last week to continue increasing monthly supply by 400,000 barrels per day in January, even after a slide in prices driven by Omicron concerns.
On Sunday, Saudi Arabia raised January official selling prices for all crude grades sold to Asia and the United States by up to 80 cents from the previous month.
Oil was also buoyed by diminishing prospects of a rise in Iranian oil exports after indirect U.S.-Iranian talks on saving the 2015 Iran nuclear deal broke off last week.
