Oil prices fell to near $91 a barrel Wednesday in Asia amid investor concern Greek voters may reject a plan to contain the country\'\'s debt crisis that was brokered by European leaders last week. Benchmark crude for December delivery was down 70 cents at $91.49 a barrel at midday Singapore time in electronic trading on the New York Mercantile Exchange. The contract fell $1 to settle at $92.19 in New York on Tuesday. Brent crude was down 51 cents at $109.03 a barrel on the ICE Futures Exchange in London. Greek prime minister George Papandreou said earlier this week that he would call a referendum vote on the agreement to cut Greece\'\'s debt level, provide the country\'\'s fresh rescue loans and require bondholders to accept 50 per cent losses. Greek labor unions have protested fiscal austerity measures, and if voters reject the debt plan, it could spark a chaotic debt default and a financial crisis. Papandreou also faces a vote of confidence in parliament Friday. The euro zone sovereign debt issue that provided a large burst of risk appetite last week has flipped to a major bearish factor this week as the Greek debt situation is suddenly again looking precarious,\'\'\'\' energy consultant Ritterbusch and Associates said in a report. Trading volumes of oil futures have been undermined this week by the bankruptcy of MF Global, a US securities firm run by former Goldman Sachs chief Jon Corzine. ``When there is a lack of activity, attrition is normal,\'\'\'\' energy trader and consultant Blue Ocean Brokerage said in a report. ``We could continue to erase gains with little volume willing to support until the market is ready to trade again.\'\'\'\' In other Nymex trading, heating oil fell 2.2 cents to $3.02 per gallon and gasoline futures slid 0.8 cent at $2.62 per gallon. Natural gas dropped 0.9 cent at $3.77 per 1,000 cubic feet.