Refinery problems in Edmonton are leading to empty pumps across Alberta. (Zulekha Nathoo/CBC)

At least two dozen gas stations in Alberta have run dry after a severe storm in Edmonton forced two refineries to shut down.

Some Esso and Petro-Canada retail stations in Calgary and southern Alberta have signs posted telling customers they are out of gas.

A major storm on July 18 that brought lightning, hail and 100 km/h winds knocked out power to the Edmonton area. The tempest forced shutdowns at both Petro-Canada's refinery in Edmonton and Imperial Oil's facility in Strathcona County.

"The [catalytic] cracker, which is a major gasoline processing unit at the refinery, experienced some damage as a result of having to do such a rapid, unplanned shutdown," explained Sneh Seetal, a spokeswoman for Petro-Canada.

Repairs were made to the plant over the weekend, and the unit is slowly returning to capacity. It normally processes 135,000 barrels of crude oil per day.

"It does take time and it is a pretty systematic, ordered approach," said Seetal.

Unit also shut down previous summer

A failure with the same catalytic cracker last summer resulted in as many as 90 Petro-Canada and independent stations in B.C. and Alberta running dry.

Seetal said on Monday that 24 of Petro-Canada's 159 stations in Alberta were empty.

The company has been shipping fuel to Alberta from its Montreal refinery and will be temporarily rationing fuel, she added.

Imperial Oil's plant, which processes 187,000 barrels a day, is also returning to full capacity after a shutdown and restart that took several days, said a spokesman.

Imperial did not disclose how many of its stations had run out of gas.