An approximate theoretical model of foam spreading on a liquid surface has been formulated. The model is analogous to the spreading of oil slicks on water surfaces. Viscous friction is assumed to be the dominating mechanism in opposing the foam spread. The friction is described by a lumped friction constant. The spreading process is decoupled from the mass transport due to evaporation and drainage of water contained in the foam. This work constitutes the first step in an attempt to formulate a model describing foam spread on a burning surface. Preliminary experiments have been carried out with foam spreading in a circular water basin without external heating. The friction coefficient is determined from experimental data. The model fits reasonably well with the experimental results for a wide range of volume flow rates and foam expansion numbers. Thus it can be concluded that the model correctly describes the basic phenomena of the foam spread.