Some Shell stations in Calgary may be out of gas until at least the end of the week. Some Shell stations in Calgary may be out of gas until at least the end of the week. (CBC)

Some Shell stations have run out of gas in Calgary amid heavy demand from summer visitors.

Supplies had been running low for a while especially during the Calgary Stampede, said Shell spokesman Jeff Gabert on Tuesday.

Shell stations in Calgary as well as other parts of Alberta could be without gas for the rest of the week, he said.

"Here in Calgary we've seen demand spikes all the way around. It's the summer driving season so there is a high demand and for us we are trying to get in as much supply in to take care of that as possible," Gabert said.

Shell is looking for other suppliers and is also bringing in gasoline from outside the province.

In October 2009, a longer than expected maintenance at a Shell refinery resulted in another gasoline shortage at retail stations in Alberta.

That summer, a severe storm in Edmonton forced two refineries to shut down leaving at least two dozen gas stations in the province out of gas.