This paper deals with the existence of weak solutions of the system that describes the two-phase two-component fluid flow in porous media. Both two-phase and possible one-phase flow regions are taken into account. Our research is based on a global pressure, introduced in3, an artificial variable that allows us to decouple the original equations. We introduce another variable that does not have physical meaning in one-phase region and name it capillary pseudo-pressure. By using these two variables we rewrite system's equations in a fully equivalent form. This allows us to derive an existence result for weak solutions in more tractable way compared to15.