The world\'s biggest watch company Swatch is looking at building a car that runs on hydrogen and oxygen, its chief executive and chairman Nick Hayek said in an interview published Sunday. \"We already have a test-car with a fuel cell,\" Hayek told newspaper NZZ am Sonntag. \"Liquid hydrogen and oxygen are used as fuel, producing very efficient combustion,\" he said, adding that the management board of Belenos -- the Swatch subsidiary building the vehicle -- has already driven around on the prototype. \"What we don\'t know is whether it would be cost-efficient to build,\" said Hayek, the son of Swatch\'s founder. 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.