The combined highway and city mileage estimate for the standard hardtop Mini Cooper is 34 miles per gallon, according to Mini USA. The supercharged "S" version of the hardtop Mini Cooper carries a 29-mile per gallon estimate.
Operating the Mini Cooper more aggressively decreases what a driver can expect for mileage numbers. However, for those who are truly economy-minded, all 2014 Mini Coopers include a selectable green driving mode, reports Motor Trend Magazine. In automatic transmission vehicles, releasing accelerator pressure between 31 and 99 miles per hour in green mode uncouples the drive train, enabling more efficient coasting. At the other end of the spectrum, the performance-tuned John Cooper Works models are rated at 27 miles per gallon and are unlikely to be driven with the goal of maximum fuel economy.