There is provided a method of operating a gas turbine engine. The gas turbine engine comprises a staged combustor having an arrangement of fuel spray nozzles in which fuel flow is biased to a subset of the nozzles adjacent one or more ignitors during a re-light procedure. The method comprises transferring heat from the oil to the fuel before the fuel enters the combustor so as to lower the fuel viscosity to 0.58 mm2/s or lower on entry to the combustor at cruise conditions. Also disclosed is a gas turbine engine.