The BMW 116d EfficientDynamics driven by the team Green-Car-Guide achieved an average fuel economy of 103 mpg UK (equal to 85.8 mpg US and 2.7lt/100km) at the RAC Future Car Challenge 2012.
This event took place between Brighton and London and it’s dedicated to vehicles such as electric, hybrid, hydrogen and low-emission conventional petrol and diesel models. The 64 mile challenge includes both uphill sections and traffic and the goal is to use the least amount of energy. 
"Being able to achieve more than 100mpg is an outstanding result and this is on top of it being the cleanest BMW ever offered for sale in the UK courtesy of 99g/km CO2 emissions" said Steve Charter, Corporate Operations Manager, BMW UK. 
The BMW 116d EfficientDynamics use a 2.0 liter turbocharged diesel engine that produces 116 bhp at 4.000 rpm and 260 Nm (191.8 lb-ft) between 1.750 and 2.500 rpm. The power is send to the rear wheels thanks to a six speed manual gearbox.  

Source: BMW