The loonie fell 0.41 of a cent to 87.64 cents US, its lowest close since July 2009.
The December crude contract in New York fell $1.59 to a three year low of US$77.19 after Saudi Arabia cut prices to its U.S. customers.
Analysts say the move added to speculation that Middle East producers are working to defend market share amid surging U.S. output.
Prices have also been pushed down by a U.S. dollar that has gained in strength lately with the conclusion at the end of October of the U.S. Federal Reserve's quantitative easing program.
Other commodity prices were also lower as investors also took in data showing the eurozone economy in precarious shape.
December copper was down five cents to US$3.02 a pound while December gold fell $2.10 to US$1,167.70 an ounce.
The European Commission has cut its growth forecast, saying growth will come in at 0.8 per cent this year, down from 1.2 per cent growth it had forecast this spring.
Meanwhile, the loonie failed to find lift from trade data showing an improvement in Canada's trade balance with the rest of the world. Statistics Canada reported the trade balance moved to a surplus of $710 million in September compared with a deficit of $463 million in August.
Merchandise imports declined 1.5 per cent in September amid declines in energy and mineral product shipments.
Exports rose 1.1 per cent, led by the vehicle sector.