IIRC, the US measure how efficient an engine burn an amount of fuel, while Europe measure the emissions of the distance traveled.
Quick and simplified example to illustrate the difference:
US car getting 33.5mpg (7.0 l/100km) emitting 126g of CO2 per kilometer. That’s 18g of CO2 per liter of fuel.
EU car getting 39.2mpg (6.0 l/100km) emitting 120g of CO2 per kilometer. That’s 20g of CO2 per liter of fuel.
It’s been years since I read about this, so I can’t remember the details of how/what it’s measured.




I had to buy a used induction stove because they no longer sell new ones with physical knobs at a reasonable price.