Canadian fuel consumption ratings show that vehicles use about 20 per cent less gasoline than U.S. estimates indicate, which has prompted the Automobile Protection Association to call for changes in Canada's ratings.

A CBC News investigation by reporter Kathy Tomlinson looked into complaints by owners of a 2011 Kia Rondo and a 2010 Toyota Yaris that their cars were using significantly more fuel than they expected.

CBC News and the Automobile Protection Association (APA) selected 13 popular 2012 models from seven vehicle classes and compared the Canadian and American fuel consumption ratings.

For every vehicle, Canada's Fuel Consumption Guide has estimates showing significantly better fuel economy than the estimates from the U.S. government. In the table below, the Canadian estimates show 16 to 22 per cent less gas is used for highway driving, compared to the U.S. estimates, for the same vehicles.

(The table compares U.S. and Canadian estimates of fuel consumption in litres/100 km for virtually identical models, all with automatic transmission. Estimates for both city and highway driving appear, followed by the percentage difference in efficiency in the Canadian estimates, compared to the American. Photos are from the U.S. Fuel Economy Guide.)

In an email to CBC News, Natural Resources Canada, the government agency responsible for the Canadian consumption guide, explained that, "Each vehicle manufacturer tests the fuel consumption of its new vehicle models and reports these results to the Government of Canada."

'Unattainable case scenarios' vs. typical driving conditions

The agency concedes that "the published fuel consumption values are achievable under ideal conditions." Or, as George Iny of the APA told Tomlinson, under "completely unattainable case scenarios."

Comparing U.S. and Canadian estimates

To compare the U.S. and Canadian estimates for a vehicle, follow these links:

Fuel Economy Guide (U.S.)

Fuel Consumption Guide (Canada)

However, the U.S. Environmental Protection Agency conducts its own tests, which they say on their website "are designed to reflect 'typical' driving conditions and driver behavior."

On Nov. 28, the APA called on the government to revise Canada's ratings, arguing the Federal Test Procedure that both Canada and the U.S. have used since the 1970s does not accurately reflect city driving conditions today. For the U.S. guide, the Environmental Protection Agency added tests using air conditioning and during cold temperature at city speeds and harder acceleration and braking at highway speeds. The three additional tests began with the 2008 models.

For highway driving, actual fuel efficiency is probably lower, according to the APA, because the tests are conducted at lower speeds than the average speed on North American highways.

Iny told CBC News that the industry promotes the "unrealistic" ratings in the Canadian guide while "they offer the same vehicle in the U.S. with a 15-20 per cent higher predicted fuel consumption." He wants the Canadian government to adopt the U.S. ratings.

The Canadian estimates are likely to change sometime soon, moving closer to the U.S. estimates and perhaps even showing lower efficiency.

"Our Government will move forward to a system more in line with the American system that takes into account the different climate issues in Canada," Natural Resources spokeswoman Jacinthe Perras wrote in the email to CBC News. Fuel consumption usually increases in very cold weather.

Drivers can improve their fuel efficiency

In her email, Perras notes that "a number of common driving habits, such as speeding, aggressive driving, air conditioner use, unnecessary idling, low tire pressure, additional weight in the vehicle, and so on can increase the fuel consumption of a vehicle."

She then adds that "external factors like poor weather conditions, congestion and variations in road conditions can also increase fuel consumption."