The falling price of oil, now trading at $85.43 US a barrel in New York , weighed on the TSX energy sector. It has fallen about 16 per cent over the last month as oil prices have also suffered from rising supplies and lower demand forecasts.
But the key worry for traders was the outlook for global growth, which was downgraded by the International Monetary Fund (IMF) earlier this week.
The Canadian dollar was down 0.34 cents to 89.17 US.
U.S. markets also had a wild week, and were mixed on Friday morning:
The Dow Jones industrial average began the day up 32 points, but was down 27 points at 10.40 a.m. ET.
The Standard and Poor's 500 index fell a point, or 0.1 per cent, to 1,926. The Nasdaq fell 32 points, or 0.8 per cent, to 4,345.
Energy stocks in the U.S. were hurt by the falling price of oil.
Electric car maker Tesla fell seven per cent in early trading as traders seemed disappointed by the company's announcement of a new all-wheel drive car late Thursday.