Fuel efficiency is a major selling point in many car ads, so consumers noticed when Hyundai and Kia were caught overstating their mileage.

The two companies are reimbursing 172,000 Canadians who bought 2010 to 2012 model vehicles, giving them pre-paid credit cards to account for the difference in real and stated fuel efficiency.

The car manufacturers are also compensating about 900,000 people worldwide.

Alex Susma was one Kia Forte owner who found the estimates were very different from reality.

"Obviously they don't really meet the expectations we get in the manual," said Susma.

The U.S. Environmental Protection Agency found the discrepancies in a random audit of test results.

"We're lucky they were and also that it happened before the vehicles were too old," said George Iny of the Automobile Protection Association.

This is not the first time Hyundai and Kia have been caught misleading car buyers. "At one point they had misrepresented the horsepower on their engines," said Iny.

But this is also an issue that is unlikely to have ever been discovered by Canadian officials.

The 2012 Fuel Consumption guide may look like it was based on Canadian government testing.

But a close look reveals it was produced by Natural Resources (and Environment) Canada in co-operation with fuel consumption data "provided" by vehicle manufacturers.

"There is no testing or very little testing by the government here," said Iny. "We rely on the Americans and when they find a problem we get the benefit of the protection."

The numbers that appear in the Canadian Fuel Consumption Guide are also based on optimum driving conditions, and can easily be off by 2 to 3 litres/100 km.

"It's false advertising with a veneer of government protection," said Iny.