Ottawa motorists will want to fill up the gas tank today, before a spike in prices at the pumps on Saturday. Gas prices dropped nine cents a litre at stations in Ottawa on Friday to around 179.9 cents a litre. Canadians for Affordable Energy president Dan McTeague says prices will increase six cents a litre on Friday. That will bring gas prices up to around $1.75 a litre. McTeague is also warning of a significant rise in diesel prices this weekend. After diesel prices increased nine cents a litre on Friday, McTeague says diesel prices will increase another 11 cents a litre on Saturday in Ottawa and across Ontario. The price of diesel will rise to $2.57 a litre on Saturday.