Saudi Arabia, the world's top oil exporter, has told refiners in Asia it would cut December supplies by 5 percent, providing the most visible evidence yet that it is adhering to OPEC's agreement last month to reduce output. [nSP414579]

U.S. crude rose $2.21, or 3.7 percent, to $63.25 a barrel by 0921 GMT, having earlier risen as high as $64.30. London Brent crude gained $2.02 to $59.37.

At the G20 group's annual meet in Brazil, finance ministers and central bank governors representing 90 percent of the world's economy vowed to take all necessary measures to get financial markets back on their feet and counter the credit crisis.

China went a step further and launched a huge stimulus plan on Sunday worth nearly $600 billion, kicking off what could be a round of big spending or interest rate cuts by leading economies to stave off a recession.

Oil lost nearly 10 percent last week and dipped below $60 the previous week, its lowest since March 2007, after a string of dismal economic data from the United States sharpened fears of a protracted recession.

The drop in prices from July's record high of $147.27 has already spurred OPEC to rein in supply from November 1, and some members of the group are talking of reducing production further.

OPEC will cut oil output again if the trend toward lower prices and slowing demand growth are unchanged when the group meets in December, Iran's OPEC Governor Mohammad Ali Khatibi told Reuters on Sunday.

(Reporting by Fayen Wong and Alex Lawler in London, editing by Anthony Barker)