The representation of magnetic saturation of generators in power system studies is re-examined in the light of new test data obtained on 500 MW and 660 MW units. A new saturation model, of adequate simplicity for use in multi-machine studies, is formulated and checked for accuracy. The parameters for use in the model are obtained firstly from no-load measurements but later in the paper it is shown that the parameters can be obtained from on-load measurements. The primary incentive for the work was to devise a method for the accurate calculation of generator rotor angle when operating at leading power factors. In the event, the model is shown to produce accurate calculation of both rotor angle and excitation requirements over the whole of the normal operating range.