VTT says that it conducted the study because many Finnish people frequently claimed that fuel consumption is significantly higher with E10 than with E5 thanks to ethanol's lower octane rating. The suspected increase in consumption has deterred many drivers from fueling with E10.
The VTT measurements show that the vehicles tested consumed an average of 10.30 liters of E10 per 100 kilometers, compared to 10.23 liters of E5 per 100 km. The difference was, on average, 0.07 liters in favor of E5, giving a meager 0.7 percent consumption increase when using E10. Now, for Americans, let's see this test conducted using our E10 and E15.
[Source: Green Car Congress]