Brent oil prices dropped to a new four-year low below $82 a barrel today, a fifth straight day of losses, as weak economic data from top energy consumer China intensified worries about demand as a global supply glut grows.

Services sector growth in China weakened in October as new business cooled, a private survey showed, coming just days after data revealed sluggish factory growth in the world's second-largest economy.

Brent fell 75 cents to $82.05 a barrel by 0913 GMT, having earlier reached the day's low of $81.63, its weakest level since late 2010.

US. crude fell 43 cents to $76.76 a barrel, rebounding off a low of $75.84 hit in the previous session - its weakest since October 2011 - after data showed U.S. crude stocks unexpectedly fell last week as refineries boosted output.

"Supply is higher and demand expectations are being cut almost every day," said Hans van Cleef, senior energy economist at ABN Amro in Amsterdam.

Brazil's oil output reached a record 2.358 million barrels per day in September, up nearly 13 percent from a year earlier, national oil regulator ANP said.

Consistent supply from Libya and Iraq, where many expected production to be disrupted by conflict, has added to the downward pressure on prices.

Van Cleef added that dollar strength was weighing on oil. Oil, priced in dollars, becomes more expensive to holders of other currencies when the US currency rises, denting demand.

The dollar index hit a new 4-1/2-year high today.