Summary A method has been developed to characterize the process of spontaneous water imbibition into gas-saturated rocks. Water relative permeability and capillary pressure can be calculated simultaneously from water imbibition data using this method. A linear relationship between imbibition rate and the reciprocal of the gas recovery by spontaneous water imbibition was found and confirmed both theoretically and experimentally, even at different initial water saturations. There was almost no effect of initial water saturation on residual gas saturation by spontaneous water imbibition. The higher the initial water saturation, the lower the imbibition rate and the ultimate gas recovery. It was found that the capillary pressure did not vary with initial water saturation in a certain range. The capillary pressure and the water relative permeability calculated using the new method was consistent with the experimental results measured using other techniques. The method developed in this paper is also of importance for scaling up experimental data.