A method of lubricating a wind turbine gearbox comprising using a lubricating composition comprising at least one (i.e. one or a mixture of more than one) perfluoropolyether (PFPE) lubricant which comprises a perfluorooxyalkylene chain, said perfluorooxyalkylene chain comprising recurring units having at least one ether bond and at least one fluorocarbon moiety. A wind turbine gearbox comprising a lubricating system containing said lubricating composition.