The performance of water flooding can be investigated by using either detail numerical modeling or simulation, or simply through the analytical Buckley-Leverett (BL) model. The Buckley-Leverett analytical technique can be applied to one-dimensional homogeneous systems. In this paper, the impact of heterogeneity on water flooding performance and fractional flow curve is investigated. First, a base one-dimensional numerical model is considered and then the numerical model is made and validated through comparison with the Buckley-Leverett fractional flow equation. Then, the model is extended to two dimensions and heterogeneity is incorporated in the modeling by using six different heterogeneous models. In particular, distributions for permeability values are considered. Fractional flow curves and water flooding performances are investigated for each individual model. A modification in the Buckley-Leverett fractional flow equation is discussed in order to consider the heterogeneity effects.