Oil prices fell on Wednesday after a big build in U.S. crude inventories which fed concerns that demand may not be enough to absorb one of the largest global surpluses in modern times.

The American Petroleum Institute on Tuesday reported a rise in U.S. commercial crude stocks of 7.1 million barrels to 473 million barrels in the week to Oct. 16, trumping expectations for an increase of 3.9 million barrels.

Rising supply from the largest-producing countries, along with slowing demand from emerging nations, has cut the price of oil in half over the last year.

With no sign that either trend will change any time soon, the oil price is more likely to fall than rise, analysts said.

"The risk is on the downside," PVM Oil Associates analyst Tamas Varga said. "It's an oversupplied market."

That is also the view of many the world's top traders, who see limited upside for oil for at least the next year.

"There is a surplus everywhere," Torbjorn Tornqvist, chief executive of Gunvor, told the Reuters Commodities Summit.

Brent crude for December LCOc1 was down 30 cents at $48.41 a barrel by 0810 ET. U.S. crude futures CLc1 for December delivery were down 65 cents to $45.64 a barrel.

Investors awaited official oil inventory figures from the U.S. Energy Information Administration, due at 10:30 a.m. ET to see if they confirmed the API data.

A Reuters poll of analysts forecast the EIA would report a build in crude stocks for a fourth straight week. 

"We've seen inventories build for the last three weeks now, which has helped ensure oil prices remain quite heavy," Oanda market analyst Craig Erlam said in a note.

"Another build today, 3.5 million barrels expected, could add further downside."

PVM's Varga said crude markets could see some short-covering as a result of a sell-off that has brought Brent down from a high of above $54 a barrel two weeks ago.

Open interest in Brent futures has risen to 442,279 lots with the rollover of the front-month contract into December, just a few thousand contracts shy of April's record, which Varga said could provide the market with a boost in the event of a larger price slide.

Only five non-OPEC countries sent officials to a meeting of with OPEC in Vienna on Wednesday to discuss possible market cooperation. The meeting was unlikely to agree any coordination over supply, an OPEC delegate said.

By Amanda Cooper - Reuters (Additional reporting by Keith Wallis in Singapore and Christopher Johnson in London; editing by Jason Neely and David Evans)