It happened at a Calgary Co-op gas station on Macleod Trail.
Customers there who thought they were pumping gasoline on Boxing Day were actually putting diesel into their tanks.
Karen Allen, who speaks for the Calgary Co-op, says it was a mistake with a delivery.
“We had a customer who had had some difficulty with their vehicle,” said Allen.
“They took it into the repair shop, who discovered the problem right away. They phoned us immediately, and we immediately shut down our pumps, started to investigate what the issue might be and then came to that conclusion.”
Allen says Co-op has already spoken with most of the drivers involved and will cover any repair costs and car rentals.