Rock pore size distribution is one of the most important parameter that can affect the reservoir depletion during the water flooding process. In this paper the effect of the pore size distribution from micro, to macro pore sizes on the capillary pressure curves, relative permeability curves and the remaining oil saturation is investigated. Gaussian distribution was developed for micro, meso and macro pore sizes assuming that the pores are bundle of tubes with cylindrical shape for simplicity. The results from capillary pressure curves illustrate the invasion paths in pores while the relative permeability curves present the rock grain sorting. Purcell’s correlation is used to calculate the data related to the relative permeability. The obtained fluid flow curves for different pore size distributions are then implemented in a simple reservoir model to evaluate the reservoir respond for water flooding. The results from simulation show that the oil recovery increases with increasing of the number of the macro pores follows by the meso and micro pore sizes. Moreover it is observed that the time of water breakthrough is highly dependent on the type of pores where the late water breakthrough time is obtained for the micro pores. This study concludes that the reservoir performances during water flooding and hence reservoir fluid production are highly dependent on the rock typing and the pore size distribution.