New York's main contract, light sweet crude for delivery in October slipped 76 cents to $94.77 a barrel and Brent North Sea crude for October delivery shed 81 cents to $112.68.
Concerns over global energy demand following a slew of manufacturing data showing weakening activity in China, Europe and the United States overshadowed the ECB plan to buy sovereign bonds, said Justin Harper, market strategist for IG Markets Singapore.
"While ECB moves to solve the eurozone crisis are welcome and saw equities rally... energy markets continue to be weighed down by weak economic data," he told AFP.
"Manufacturing data has been weak and that shows the economy is still very sluggish and will keep a cap on oil prices," Harper added.
Traders were also disappointed after positive US jobs data released late Thursday suggested the Federal Reserve would likely delay any moves to introduce another round of stimulus measures, Harper said.
Traders are now looking ahead to the release of non-farm payrolls data later Friday for more clues about the state of the world's leading oil consumer, he added.