Dips in demand and an easing of threats to supply have pushed oil prices to a seven-month low.
Traders had been worried about a repeat of last year's storm damage
US light, sweet crude futures traded down $1.85 to $63.76 a barrel on Tuesday while Brent crude futures slid $1.56 to $62.99 a barrel in London.
Prices have fallen by almost 18% from the $78-a-barrel highs recorded in mid-July at the height of the crisis between Israel and Lebanon.
Concerns that the US hurricane season would damage oil rigs proved unfounded.
Damage to refineries, offshore rigs and pipelines from Hurricane Katrina last year pushed oil prices to new records.
Traders are increasingly doubtful that Iran's diplomatic stand-off with the UN over its nuclear ambitions would lead to it using its oil as a bargaining chip if sanctions were imposed against it.
On Monday, the Opec cartel of oil producers said it would continue producing oil at current levels but added it would scale back production if prices kept falling.