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"We've had disappointing data from China and Europe, and US crude inventories are high, so there's plenty of supply, but tepid demand," said Michael Hewson, chief market analyst at CMC Markets.
Brent crude futures fell 42 cents to $77.68 a barrel at 10:57 GMT after closing 37 cents down in the previous session.
It was heading for its lowest close in four years and has fallen a third from its peak for the year in June.
US crude oil for December delivery was down 25 cents at $74.33 a barrel, after finishing down three cents on Wednesday. The December contract expires on Thursday.
A survey showed euro zone business growth weaker than any forecaster expected this month and new orders down the first time in more than a year, while a survey of China's manufacturing also came in weaker than expected.
Oil investors are closely watching comments from Opec members to try to establish the likelihood of a possible cut to supply ahead of next Thursday's meeting.
According to Samir Kamal, Libya's OPEC governor and head of planning at the Libyan oil ministry, ministers from the oil producers' cartel will agree to scale back production to Opec's own target of 30 million barrels a day at the November 27 meeting.
That would result in a cut in output of between 250,000 and 600,000 barrels a day in an effort to buoy oil prices.
Iran will double its oil exports within two months if sanctions against it end, Oil Minister Bijan Zanganeh told official news agency IRNA.
"Under no circumstance will we reduce our global market share, even by one barrel," he said.
The market was also waiting for a slew of economic data from the United States later on Thursday, including consumer prices for October.
US crude stockpiles unexpectedly rose by 2.6 million barrels last week, supported by an increase in oil imports, data from the U.S. Department of Energy's Energy Information Administration showed on Wednesday.
