The Shell Eco-marathon (short SEM) is the world’s biggest energy efficiency competition which takes place in London every year. For the contest students from Europe and Africa construct a vehicle with the goal to reach 15km using the least amount fuel as possible.
Alongside London the Shell Eco-marathon also takes place in Detroit and Singapore, with more then 450 student teams participating worldwide. Two primary types of engines are used in the competition, fuel motors and electric engines. After the race, the fuel/electric consumption of the engine is measured. With the results being calculated based on how far the vehicle would get as if it had only used one litre of fuel or the equivalent of electricity. The vehicle that has used the least fuel is then declared the winner of the competition and thus the most efficient vehicle.
You can find detailed information for each year here: