The instant invention relates to a process for controlling the viscosity of organic liquids by incorporating in said liquid a minor amount of polymer complex, and optionally a cosolvent for the ionic groups of said polymer. The polymer complex comprises the reaction product of a metal neutralized sulfonated polymer and a basic nitrogen-containing polymer, wherein the polymer complex is substantially soluble in said organic liquid, and pendant sulfonate groups which are substantially insoluble in said organic liquid. The optional cosolvent is selected which will solubilize the pendant sulfonate groups and provide a reasonably homogeneous mixture of solvent, cosolvent and polymer complex. The preferred compositions prepared by the method of the instant invention comprise an organic liquid having a solubility parameter of from 6 to 10.5 in combination with a polymer complex containing from 0.2 up to 10.0 mole % sulfonate groups and nitrogen-containing groups, and optionally a nonvolatile alcohol or amine cosolvent.