Small aviation develops very dynamically. This is a result of airplane general availability and their lower prices. At the same time, however, the maintenance costs of airplanes increases. It particularly concerns the operation cost where fuel is its substantial part. At the moment special 100LL gasoline is used to fuel aircraft piston engines. It is about 20% more expensive than ES95 gasoline of comparable properties. The paper shows the results of test-bed research conducted on the radial piston aircraft engine fuelled by aircraft 100LL gasoline and automotive ES95 gasoline. The object of research was ASz-62IR engine by WSK Kalisz fitted with an experimental fuel injection system. The power, fuel consumption and cylinder head temperatures were analysed in the selected typical operating points. The testing was carried out in a steady state. It was proven that it is possible to exchange (replace) fuels with no engine power loss with a miniscule increase of fuel consumption.