US light, sweet crude for October fell $1.15, to $105.19. London Brent crude dropped $1.17 to $102.27.
Prices have sunk from a record of more than $147 a barrel seen in July.
Opec members have expressed worries about waning energy demand - especially in the US - as a world economic slowdown takes its toll.
"If the market is coming to a view that Opec will not be doing anything at all, then I think you might see oil prices lower and I think that is what's happening right now," said David Moore, strategist at Commonwealth Bank of Australia.
Growing demand
"The market is fairly well balanced," said Saudi Oil Minister Ai al-Nuaimi.
"Inventories are in a healthy position, everything is in balance."
OPEC members including Kuwait and the United Arab Emirates, have called for no change in output levels though Algeria, Iran, Venezuela and Libya have suggested a cut is needed - claiming the market is oversupplied.
Opec is currently thought to be producing about a million barrels per day (bpd) more than its official ceiling of 29.67 million bpd.
In May and June Saudi Arabia agreed to increase production by 500,000 bpd to help calm markets.
In July, the exporters' group said world demand for oil would grow by 50% between now and 2030 as people in developing countries drive more cars.




