||This paper deals with hydric transport in partially saturated COx argillite, a low permeable porous rock. Our work is based on the monitoring of mass vs. time in a controlled environment, in relative humidity due to the method of saturated saline solution. Our study aims at understanding and analyzing the measurements of transient mass loss of a sample submitted to a decrease of relative humidity in a hermetic chamber. In this aim two models are proposed. The first model takes into account liquid water, water vapor and dry air in the porous network, whereas the second model accounts only for the Darcian flow of the liquid phase. Based on the numerical implementation of the first model, a scenario is proposed for the physical phenomena occurring during a drying test. In doing this study and analysis, gas effective permeability of COx argillite is obtained by direct measurements and water effective permeability is identified in the frame of both models as the solution of an inverse analysis. These values of gas and water effective permeabilities provide a better knowledge of the transport properties of COx argillite. It is shown that the simplified approach is satisfactory to obtain the correct order of magnitude of the water effective permeability for COx argillite.