Light, sweet crude for October dropped to $105.19 yesterday, while London Brent crude fell $1.17 to $102.27.
This is a far cry from the all-time high of $147, set in New York earlier this year.
When it meets in Vienna, Opec countries are expected to agree to maintain current production levels.
Ai al-Nuaimi, Saudi Arabia's oil minister, has already commented that the market remains "well-balanced" at the moment - boosting hopes of further price stabilisation.
Hurricane Gustav did not disrupt the US Gulf's oil supplies as significantly as had been feared.
The strengthening dollar is another factor behind the falling price trend.
Speaking to the BBC David Moore, a strategist at Commonwealth Bank of Australia, added: "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."