A fractional flow formulation is proposed to model two-phase flow in heterogenous porous media in the case of low interfacial tension. The proposed formulation overcomes the limitations of the fractional flow approach that arise from saturation discontinuity. The total velocity is calculated with two terms. A total mobility term multiplied by the non-wetting phase potential which is a smooth term over the computational domain. The second term is the buoyancy term that represents the density contrast between the two phases. The proposed formulation is verified with the Buckely--Leverett analytical solution. Two other numerical examples are presented in 2D and in 3D. The examples show the applicability of the model in anisotropic and in heterogenous porous media and demonstrate the low mesh dependency of the model.