Abstract: In a process for the separation of oil from an oil-in-water dispersion by coalescence followed by separation of coalesced drops, coalescence is carried out at the surface of a solid material manufactured by contacting a solid material having active H atoms in surface groups or a polyolefin in the presence of water with a compound Si(R.sup.1)(R.sup.2)(R.sup.3)(R.sup.4), in which R.sup.1 is a (cyclo)aliphatic group containing one or more amino groups, R.sup.2 a hydrolyzable group and R.sup.3 and R.sup.4 a hydrolyzable or non-hydrolyzable organic group or a hydrolyzable atom.