TORONTO - An extended shutdown at a Shell refiner in Sarnia has led to a gas shortage in Ontario, the Toronto Sun reports.

Additionally, the disruption of operations at an Esso Imperial Oil refiner in Nova Scotia, which has affected fuel supply at many Nova Scotia stations, is also contributing to the Ontario shortage.

"One of the things that happens when a big refinery goes offline for awhile is that it has ripple effects regionally and you start pulling in gas from other areas to compensate for the loss in supply of gas and if it drags on for a couple of weeks, other issues can exacerbate," said Jason Toews, cofounder of Gasbuddy.com, adding that when gas begins running out at stations, customers begin to panic and purchase fuel for the future.

"If millions of people start panic buying, other gas stations start to run out of gas even though the gas refineries are operating normally," Toews said.

Shell Canada spokesperson Jeff Gabert said the company€™s Sarnia refinery underwent a standard maintenance shutdown, which lasted a week longer than anticipated.

"We still have quite a few sites at any given time be out of bronze fuel or out completely ... at any given moment in Toronto, London and Sarnia. All three cities are affected with the majority of sites without fuel being in the GTA," Gabert said. "The Sarnia refinery is back up and running ... We€™re working as quickly as possible to get them to the stations."

An OLCO service station on Kipling Ave. in Toronto ran out of gas earlier this week. "Right now we€™re open, but we have no gas to sell," said a station clerk.

Other stations across the greater Toronto area have been out of fuel for five days or longer.