This paper presents a theoretical analysis of the experimental evidence reported in papers 1 and 2 (Lu et al., this issue (a, b)). The analysis of force is conducted on spherical particles serving as an idealized porous medium. Four close packing conditions were studied and two models were developed to describe liquid movement in glass bead porous media. According to the analysis of forces acting on the contact point of gas-liquid interface, the direction as well as the magnitude of the total surface tensile force changes in contrast to a constant total surface tensile force acting in a capillary tube. It is shown that the velocity of the liquid plays an important role during capillary rise into porous media. Equations for the height and velocity of capillary rise into initially dry porous media are given for four different geometries of close packing. The models and equations present an improved explanation of the Haines' ''jump'' phenomenon and the instability observed in experiments of capillary rise in porous media. ¿ American Geophysical Union 1995