Consumer Reports in the US reckons Ford's fuel economy claims for the new 2013 Fusion Hybrid and C-MAX Hybrid are "eye-opening" and that its "real-world tests", though achieving "very good results", were far below the automaker's "ambitious triple-47 figures" - it claims "47 city/47 highway/47 combined mpg".

In the consumer advocate's tests, the Fusion Hybrid achieved 39mpg overall and 35 and 41 in city and highway conditions, respectively. The C-Max Hybrid got 37mpg overall, with 35 and 38 for city and highway.

"These two vehicles have the largest discrepancy between our overall-mpg results and the estimates published by the EPA that we've seen among any current models," Consumer Reports said in a report published on its website.

CR noted the disclaimer on EPA fuel-economy labels notes that "your results may differ." But the overall mpg for these C-Max and Fusion models is off by a whopping 10 and 8mpg, respectively, or about 20%.

"Our overall-mpg results are usually pretty close to the EPA's combined-mpg estimate. Among current models, more than 80% of the vehicles we've tested are within 2mpg. The largest discrepancy we've previously seen was 7 and 6mpg for the Toyota Prius C subcompact and Prius hatchback, respectively."

Nonetheless, the overall conclusion was complimentary: "...both the Fusion Hybrid and C-Max Hybrid still deliver excellent fuel economy. The Fusion Hybrid's 39mpg is the best of any family sedan we've tested.... And the C-Max Hybrid's 37 mpg is second only to the Prius V's 41 mpg in its class.

"But our tests show that buyers shouldn't expect the stellar 47 mpg that Ford is promoting."

Hyundai Motor and affiliate Kia Motors were recently accused of overstating fuel economy claims in the US. The South Korean government said recently it would make it compulsory for local carmakers to disclose vehicles' fuel economy starting in the second half of next year.

UK buyers have also found discrepancies between their cars' real-world fuel economy and the figures claimed by automakers in 'official' lab-based tests. Websites such as Honest John and What Car? now have pages devoted to reporting data based on reader feedback. Honest John's 'Real MPG' reckons models sold in the UK achieve on average 88% of their 'official' mpg (UK imperial gallons, incidentally, at 4.54 litres are larger than the 3.9-litre US gallon).

What Car?, whose site is linked to the Tesco supermarket petrol station chain, offers 'true MPG' data for a variety of cars and tips on economical driving.