A first order correction to the force over an isolated spherical particle in inviscid flow is presented, considering binary sphere-sphere interactions. The two-particle distribution function derived by Drew and Mandyam (1998) is used to calculate the effect of the presence of other particles surrounding a test particle. The calculations are performed for a monodisperse distribution. The introduction of first neighbor particle-particle interactions results in the prediction of forces that depend on particle concentration and concentration gradients. For the case of non-accelerated sphere we obtain forces that oppose particle concentration. When the particles are accelerated we obtain an increase of the virtual-mass coefficient with particle concentration.