British and American cars express fuel consumption of cars in "miles per gallon" (mpg). Unfortunately they don't use the same gallon. The Imperial gallon, still sometimes used in metric Britain, is 4.542 litres, whereas the US gallon is somewhat smaller, at 3.785 litres. So a car which does 30 mpg in England achieves only 25 mpg in the States.
 
The rest of the world uses either kilometres per litre or litres per 100 km. 25 US mpg is equivalent to 10.63 km per litre. Usually this is turned upside down and expressed as 9.41 l/100 km.
 
This inversion, or reciprocal, is generally a better way of expressing fuel consumption as vehicles get more and more efficient. Imagine you have a fuel consumption gauge in your car and you average 8 l/100 km. As you start going downhill it may drop all the way down from 8 to 4 to 2 and to zero, i.e. no fuel is being used at all. With the old way of measuring consumption, you would go from 12.5 km/l to 25 to 50 and to infinity (infinite distance per unit of fuel), which is not only a bit odd, but means your gauge would have to be drawn as a logarithmic scale instead of the nice and easy linear one with the inverted units.
 
Colin