Oil prices extended losses and fell closer toward $68 a barrel on Thursday, as data showing an unexpectedly high build up in U.S. oil and products stockpiles reminded traders that oil prices may have run ahead of the demand fundamentals.

Crude oil prices fell nearly 4 percent in the previous session and are on track to shed about 5 percent this week, as demand concerns resurface.

U.S. crude for November delivery fell 44 cents to $68.53 a barrel by 10:37 p.m. EDT, after settling down $2.79 on Wednesday.

London Brent crude fell 39 cents to $67.60 a barrel.

A few factors were at play last night and the most notable was the U.S. inventories number and that was unambiguously bearish, said Toby Hassall, a commodities analyst at CWA Pty Ltd in Sydney.

A bounce in the U.S. dollar and a weak equities market also combined to exacerbate oil's fall on Wednesday.

The market has been very well supported by the recent economic optimism and the falling dollar, but the latest EIA numbers show there's that underlying downside risk for the oil market, Hassall said.

The U.S. Energy Information Administration reported commercial stockpiles of crude rose 2.8 million barrels in the week to September 18, against analysts' expectations of 1.5 million barrels fall. <

Gasoline inventories increased by 5.4 million barrels to 213.1 million, and distillates gained 3.0 million to hit a 26-year high of 170.8 million, according to the EIA.

The worst global recession since the Great Depression has battered demand in the United States and other big consumer nations, shaving crude prices off record highs near $150 a barrel struck in July 2008 to below $33 a barrel in December.

But with prices having risen about 54 percent this year to reach a 2009 high of $75 a barrel in August, amid ebullience on the economic outlook, most analysts feel some convincing evidence of a recovery in global demand is now needed to push oil out of the top of the $68-$75 price range where it has traded in the third quarter.

BNP Paribas also cautioned that a recent string of positive economic data could potentially overstate actual growth as it was hard to distinguish if the rebound in indicators, such as factory output, was merely reinstatement of previously canceled orders or a genuine return to growth.

Industrial output is recovering after undershooting final demand but the improving surveys could potentially overstate actual growth as the economy comes back from the lows of Q1 and Q2, BNP's senior analyst, Harry Tchilinguirian, said in a report.

Analysts said investors would keep a keen watch on some key economic data due to be released later on Thursday, including weekly U.S. jobless claims number and August home sales data, to get more clues on the pace of recovery in the world's largest energy consumer.

(Reporting by Fayen Wong; Editing by Clarence Fernandez)