Brent ended the session up 2.09 percent at $50.89. The session high of $51.05 was its highest since June 23.

U.S. crude settled at $48.22, up 3.06 percent after touching a session high of $48.38, the highest since July 5.

Both benchmarks have risen more than 20 percent from a low in early August on news the Organization of the Petroleum Exporting Countries (OPEC) and other key exporters will probably revive talks on freezing output levels when they meet in Algeria next month.

The rapid rise puts oil, technically, in a bull market.

The rally has also been driven by short covering by speculators including hedge funds and other money managers, who had amassed record short positions.

A weak dollar also provided support to greenback-denominated oil. Against a basket of currencies, the dollar fell 0.6 percent and hit an 8-week low versus the Swiss franc.

Many OPEC members have been hurt badly by a collapse in oil prices over the last two years. While some Gulf oil exporters have very low output costs, other producers such as Iran and Venezuela need oil prices above $100 to balance their budgets.

"With the lack of investment from outside oil companies, the sovereigns will be the best hope to raise production next year in a situation where it is likely that demand will exceed global output and that in and of itself is a reason that a production freeze at current levels still matters," said Phil Flynn, senior energy analyst at Price Futures Group.