A drive system for a vehicle comprises an electrical machine, arranged between a combustion engine and an input shaft to a gearbox. The rotor of the electrical machine is connected with a component of a planetary gear, and the input shaft of the gearbox is connected with another component of such planetary gear. A first locking means may be moved between a locked position, in which the planetary gear's three components rotate at the same rotational speed, and a release position, in which the components are allowed to rotate at different rotational speeds. A second locking means is moveable between a locked position in which the output shaft of the combustion engine is locked together with a component in the planetary gear, and a release position, in which the combustion engine's output shaft is decoupled from such a component.