[en] A simple phenomenological model of the regulatory coupling between the star formation rate and the molecular gas fraction is presented. The model can in a qualitative way explain both the constant star formation rate observed in most galaxies and the starbursting behaviour seen in some systems. Formation of massive stars are thought to have both a positive and a negative feedback on further stellar formation. A sudden increase in the gas available for star formation will cause a strong increase in the star formation rate lasting for ∼ 3.10⁷ yrs. Both the star formation rate and the molecular gas friction will then perform damped oscillations over a period of a few x 10⁸ yrs. This general behaviour is valid for a large range of parameter values