The last decade has been one of the most interesting in the history of the automobile as governments task automakers to build cleaner cars even as customers clamor for more power. Amazingly, companies like Ford have managed to pull off this impressive feat for the most part, delivering dramatically more efficient cars compared to the rides of a decade ago, even as horsepower levels reach nigh unfathomable levels.

But as Green Car Reports uncovered, the devil is in the details, especially when it comes to Ford. Upon closer examination, it was revealed that the Lincoln MKX with the 2.7 liter EcoBoost engine was tested using 93 octane for its horsepower rating, but 87 octane with 0% ethanol for its fuel economy sticker.

Ford testing the 2015 Mustang’s horsepower using 93 octane, which is unavailable in many parts of the country.

As car enthusiasts we all know that higher octane fuels contain more energy, thus creating more power; in the case of the MKX, it has ratings of 335 horsepower and 380 lb-ft of torque using 93 octane. The problem is that this fuel isn’t available in many states, especially on the West Coast which has more stringent emissions standards than the rest of the country. The MKX also recommends using regular 87 octane fuel, rather than the premium gas that can cost 50-cents a gallon more at the pump. Ford used 93 octane to arrive at the horsepower figures of the 2015 Mustang, we should note.

Yet Ford then went and used 87 octane with 0% ethanol for test its fuel economy, receiving a rating as high as 17 city/26 highway 21 combined for the EcoBoost/front-wheel drive model. However, Ford opted to use a 100% gasoline blend of 87 octane for that rating, even though the EPA automatically corrects the fuel economy 10% downwards to account for the fact that most stations only offer E10, a 10% blend of ethanol and 90% gasoline. Ethanol has a lower energy output, resulting in lower fuel economy.

In other words, there’s no real reason for Ford to test the way they do, though automakers are always looking for ways to eek out even the smallest advantage over competitors. Ford has been called out for its optimistic MPG numbers before, resulting in a quick mea culpa and a small refund to customers. At least in the case of 2015 Mustang EcoBoost though, the published numbers and what people are actually getting on the road seem to line up.

In Ford’s defense, it’s certainly not the only automaker to use this tried-but-true method of bolstering horsepower and fuel economy ratings. In Europe it’s actually become something of a running gag with how much automakers like Mercedes try to rig the system, taping over body panel gaps and boosting tire pressure, sometimes landing ratings that are 40% better than what their cars are actually capable of. That makes Ford’s use of different fuels look almost amateurish in comparison.