The present invention relates to a process for the viscosification of an organic liquid which comprises the steps of forming a first solution of an anionic polymer dissolved in the organic liquid; forming a second solution of a cationic polymer dissolved in the organic liquid; and mixing the first and the second solutions together to form an interpolymer complex of the anionic and cationic polymer in the organic liquid, wherein the organic liquid containing the interpolymer complex has improved viscosification properties. This solution possesses higher viscosity than the mean of the separate viscosities of the starting solutions at relatively low solids content. Moreover, these interpolymer complexes, in hydrocarbon solutions, can be formulated to exhibit shear thickening at increased shear rates. This property is useful in such technological applications as antimisting of the solvent.