Oil prices have extended their falls from the end of last week amid continuing concerns about the Greek debt crisis and the weak US recovery.
The International Energy Agency's decision to release emergency reserves last week has also depressed prices.
On Monday Brent crude for August delivery fell $2.95 to $102.72 a barrel, while US light, sweet crude dropped $1.13 cents to $90.14 a barrel.
The strengthening US dollar has also depressed prices.
Attention is now turning to economic data due out in the US on Friday.
The Institute for Supply Management is expected to report that factory activity slowed in June from May's level, which was already the slowest since September 2009.
"The market is trying to pre-empt Greece and worries in the West," said Jonathan Barratt from Commodity Broking Services in Sydney.
On Thursday the IEA announced that it was to release two million barrels of oil a day over 30 days, partly to replace lost production from Libya.
The Greek parliament is debating austerity measures on Monday, ahead of a crucial vote on Wednesday.