New British petrol standards will soon allow oil companies to double the amount of ethanol in the fuel you put in your car.
The aim is to cut greenhouse gases, but estimates are that an increased ethanol level will have a detrimental effect on fuel economy.
At the moment, the petrol you buy on garage forecourts could contain anything up to 5% ethanol, but companies have been allowed to include up to 10% ethanol since March 2013, although none have yet made the move.
We tested the new so-called E10 fuel against pure, E0 petrol to see what the effects were on efficiency and emissions.
Read more about our investigation into E10 here
Read about our tests and the results
Read more about when E10 is likely to come to the UK