 The rapid dieselisation and electrification of Victorian Railways' mainline operations in the 1950s meant that the X class was rendered obsolete as the new B class diesel-electrics and L class electrics proved their superiority over steam for heavy freight work.Withdrawals commenced in 1957 and accelerated with the delivery of the S class diesel-electric locomotives from August that year, with the diesel fleet by then large enough for the X class to be displaced from mainline goods haulage.A report comparing total operating costs per mile (including fuel, oil, crewing, maintenance, depreciation and interest) for locomotives in freight service found an S class diesel-electric cost 68.41 pence per mile versus 261.01 pence per mile for the X class steam locomotive.