The invention relates to an oil management system for a compressor in a refrigeration system comprising: an oil temperature sensor; a heater arranged to heat oil in a crank case of the compressor; and a controller operatively associated with the temperature sensor and the heater, the controller arranged to control operation of the heater on the basis of ambient air temperature and oil temperature to maintain the oil temperature within a range Tmax≧R≧Tmin where Tmax>Tmin.