After an oil change, my car is now completely back to normal. It idles smoothly, and gets the expected fuel economy. After I entered the USA and started buying gasoline there, my fuel economy dropped by 10 to 15% and stayed low for the whole length of the trip. Upon returning to Canada, my fuel economy returned to normal. How could the oil companies do this kind of thing? I tested my car again today, and scored 35.4 mpg, which is close to what I was getting on Canadian gas before the trip. Is there anyone here who has access to a bomb caloriometer, who can accurately measure the heating value of the current gas formula and compare it to some gas bought in Canada? I'm curious if the energy content is 10% less in the USA. Would this make front page in the newspapers if it could be confirmed?