By assigning target values (0.15 Omega cm(2)) for the performance of the individual components in a single SOFC cell it has been possible to propose a very simple model which relates experimentally accessible parameters, such as, oxygen surface exchange coefficients (k cm . s(-1)) and self diffusion coefficients (D* cm(2) . s(-1)) to the behaviour of porous oxide cathodes. Characteristic lengths including a collection length (l(c)), and a maximum length (l(t)) for bulk diffusion of oxygen ions, have been defined and calculated for La0.8Sr0.2O3+x, La0.8Sr0.2Co0.2Fe0.8O3-x, Sm0.6Ca0.4CoO3-x. These characteristic lengths have been used to interpret the reported behaviour of the oxide electrocalalysts and to suggest modifications which could improve their performance. Although a similar model has not yet been developed to interpret the behaviour of anodes, appropriate comments have been made about the selection and optimisation of anodes for intermediate temperature (500-750 degrees C) SOFC operation.