Well, many years back, Honda sent cars to the EPA for the mileage testing. Oops, they got caught-had Mobil 1 in the engines. Disqualification, since that was not the factory installed oil.
Fleets have shown mileage improvements of 3-5% for decades. Individuals have found anything from zip to over 10%. But then, we all know that is impossible, huh?
Gee, dyno tests show increased horsepower! Wow, that means I can get more zip, but I don't get any better fuel economy. Duh!
Yep, must be the gas, or the weather, or global warming (did you catch the report on core samples from the north pole region which showed evidence of tropical weather?), or a great tail wind-