Recently Alexander suggested modifications to the inviscid theory of Stanton Jones for improving the agreement between theory and experiment on the cushion pressure of hovercraft. However, these simple inviscid theories can hardly be expected to represent even approximately the behaviour of peripheral jets in hovercraft and a more plausible theory taking mixing into account can easily be developed from some work of Bourque and Newman on the re-attachment of plane jets to adjacent surfaces. This theory, which is somewhat similar to a theory of Chaplin, can be used to predict the behaviour of peripheral jet models both in and out of ground effect but it is the intention here simply to compare the predictions of the mixing theory in ground effect with the simple inviscid theories which seem so commonly used in cushion craft work. Also, the advantages and potential of the mixing theory will be discussed briefly.