Ottawa motorists will want to fill up the gas tank today before prices increase on Thursday. Canadians for Affordable Energy president Dan McTeague says gas prices will increase six cents a litre at Ottawa gas stations on Thursday to $1.89 a litre. Prices went up one cent a litre on Wednesday. Meantime, McTeague is warning the cost of diesel will jump 14 cents a litre on Thursday. In Ottawa, the average price of diesel will be 268.9 cents a litre. Diesel prices have increased from $2.47 a litre in Ottawa last week.