It's frustrating buying a car to find its gas mileage falls short of the official EPA ratings, and it's a frustration quite familiar to owners of the 2013 Ford C-Max Hybrid.

The car was launched to much fanfare with its 47 mpg combined rating--identical to that of the Ford Fusion Hybrid--but it didn't take long for owners and press alike to discover that real world economy could miss the publicized number by as much as 20 percent.

Ford placed the blame at the foot of the EPA's testing procedure, supposedly unrealistic for hybrids--but after re-testing several hybrid vehicles, the EPA has come back with a clear message: "The problem here is really not how the testing is done."

Speaking to Automotive News, the Agency said its re-testing of certain models to determine the accuracy of its testing was "quite reassuring". Experiments with the Toyota Prius and Hyundai Sonata Hybrid on the same tests that faulted the C-Max showed each was capable of meeting its official figures. These results seem to be backed up by real-world figures too--as owners on sites like the EPA's and independent Fuelly are recording numbers within a few mpg of the EPA's combined rating. As we've found out in the past, some vehicles do better than others at meeting official claims.

Some put the C-Max's issue down to the way it was tested, making use of an out-dated rule that allows automakers to apply the same figures to different cars if they share the same drivetrain. Using this method, the C-Max is simply given the Fusion Hybrid's numbers, regardless of other differences between the two vehicles.

Toyota could have done the same with the Prius and Prius V wagon--but chose not to. It defends the EPA's latest comments.

"Toyota agrees with EPA that this is a not a hybrid issue, but strictly an issue of how the Ford C-Max Hybrid fuel economy values were determined" it said in a statement, according to Automotive News.

Ford is less convinced, calling it an "industrywide issue" for hybrid vehicle fuel economy. The company says the regulations create anomalies for hybrid vehicles.

Earlier this month, Ford cut the C-Max Hybrid's official figure from 47 mpg to 43 mpg--bringing it closer to the real-world numbers experienced by owners. It also announced refunds of $550 and $325 to those who'd bought and leased the car respectively. Spread across the car's 32,000 drivers, it's costing Ford $10 million to $16 million.

Small mechanical changes to the car for the 2014 model year--not offered to customers of earlier cars, unlike the firm's software updates--should also help improve its economy.


Follow GreenCarReports on Facebook, Twitter, Instagram and Google+