A method of operating a gas turbine engine. The gas turbine engine includes an accessory gearbox arranged to power one or more engine accessories, and a combustor in which fuel is combusted and a fuel-oil heat exchanger arranged to transfer heat between oil and fuel that is provided to the combustor. An average temperature of lubricating oil is at least 180° C. on exit from the accessory gearbox at cruise conditions. The method includes transferring heat from the oil to the fuel before the fuel enters the combustor so as to raise the fuel temperature to an average of at least 135° C. on entry to the combustor at cruise conditions. Also provided is a gas turbine engine.