The effect of gas adsorption on van der Waals forces has been studied theoretically using the Hamaker theory. The calculated results show that the adsorption of CO2 on FCC particles increases the van der Waals forces by 1 to 2 orders of magnitude, corresponding to pressure from 1 to 15 bar at room temperature. The effects of particle deformation have also been studied using the Hamaker theory by integrating molecular interactions over two deformed spheres and a new equation has been derived. The effects of surface roughness have also been studied using a ’sandwich’ model of the contacting system and the results show that, for FCC-FCC contact, particles could be treated as smooth when the surface asperities are less than 0.01 mu m; however, it is the surface asperities rather than the parent particles which begin to dominate the van der Waals forces when the surface asperities are more than 0.1 mu m.