Conversion of 26 MPG (USA) in L 100km (liters/litres per 100 km) is 9 liters per 100km. Cars that get 26 mpg in USA would consume 9 liters of petrol if it was driven for 100 km in Europe.
If in the UK and you are asking how many litres per 100 km would be consumed for a 26 mpg car (UK) in imperial measure, then we would convert 10 UK mpg as 10.9 litres per 100km. This means that a 26 mpg car in the UK would consume 10.9 litres of petrol if driven for 100 km.
Just to clarify:
26 MPG (USA) = 9 L in 100km
26 MPG (UK) = 10.9 L in 100km
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