Weak economic activity is adding to fears of deflation, with euro zone inflation data due later on Wednesday expected to show the first annual fall in consumer prices since 2009.

Brent crude oil fell below $50 a barrel for the first time since May 2009 on Wednesday, hammered by a growing supply glut and weak global demand.

The pace of global business growth eased to its weakest rate in over a year at the end of 2014, according to JPMorgan's Global All-Industry Output Index, produced with Markit.

Weak economic activity is adding to fears of deflation, with euro zone inflation data due later on Wednesday expected to show the first annual fall in consumer prices since 2009.

Benchmark Brent crude futures were down 85 cents at $50.25 by 0916 GMT, having fallen as low as $49.66, a level last seen in May 2009.

US futures were down 40 cents to $47.53 a barrel, having fallen to $46.83, their lowest since April 2009.

Oil markets are down for a fifth straight session and off by more than 10 per cent this week.

Prices have lost around 57 percent since their peak above $115 last June as stockpiles of oil mount with no signs of a cut in production from OPEC.

"There's a surplus in production of 1-1.5 million barrels per day in 2015 and there's absolutely no sign OPEC will intervene to cut production at a time of lower demand," said Bjarne Schieldrop, chief commodity analyst at SEB in Oslo.

He added that there was also little sign that prices at these levels were likely to have an impact on US shale production.

The slide in oil prices has increased fears of deflation, which in turn has further clouded the demand outlook.

Nobuyuki Nakahara, a former oil executive and ex-member of the Bank of Japan's policy board, told Reuters he expected further price falls.

"Oil prices are likely to keep falling due to slower Chinese growth and because the years of prices above $100 before the recent plunge were 'abnormal' historically," he said.

"I would not be surprised if the price falls to as low as around $20," he added.

(Additional reporting by Henning Gloystein in Singapore and Yoshifumi Takemoto in Tokyo)