An extension of the concept of the load supplying capability of an electrical power system is proposed, which involves drawing a capability chart. The method for obtaining such a chart is based on an optimisation model, which is repeatedly solved to obtain the points for the chart. The uncertainties which affect the nodal load forecasts are taken into account. The application of the method to a test system is described. The chart is drawn for different system configurations as is required in planning studies that aim at obtaining the maximum power which can be effectively supplied to the loads.