One of the world's biggest watch companies, Swatch, wants to build a car that runs on hydrogen and oxygen.Its chief executive and chairman, Nick Hayek, said in an interview with NZZ am Sonntag: "We already have a test car with a fuel cell. Liquid hydrogen and oxygen are used as fuel, producing very efficient combustion."The management board of Belenos, the Swatch subsidiary building the vehicle, has already driven the prototype.COST-EFFICIENT?Hayek, son of Swatch's founder, admitted: "What we don't know is whether it would be cost-efficient to build." “Liquid hydrogen and oxygen are used as fuel, producing very efficient combustion,” he said.Hayek confirmed that the project was being overseen by subsidiary clean-energy company Belenos.Belenos has reportedly been working on the vehicle with Swatch since 2008, and a concept version, known as a the ELV2, has already been revealed. The ELV2 is powered by a 40kW electric motor mated to a lithium-ion battery pack and charged by a hydrogen fuel cell.The fuel-cell vehicle is not Swatch's first attempt at building a green car. In 1997 it teamed up with Daimler-Benz to build the two-seater Smart but the watch firm later sold its shares to Daimler-Benz.