A method for scavenging mercaptans in a hydrocarbon fluid is disclosed. According to the method, an effective mercaptan-scavenging amount of an aqueous scavenging composition is added to the fluid. The composition comprises a quaternary ammonium hydroxide of the formula R.sup.1 R.sup.2 R.sup.3 R.sup.4 NOH. R.sup.1 and R.sup.2 are, independently, alkyl groups of from one to about eighteen carbon atoms, aryl groups of from six to about eighteen carbon atoms or alkylaryl groups of from seven to about eighteen carbon atoms. R.sup.3 is an alkyl group of from two to about eighteen carbon atoms, an aryl group of from two to about eighteen carbon atoms or an alkylaryl group of from four to about eighteen carbon atoms. R.sup.2 and R.sup.3 may be joined to form a heterocyclic ring including the N and optionally an oxygen atom. R.sup.4 is --(CH.sub.2 CH.sub.2 O).sub.n H, wherein n is an integer from one to about eighteen, or --CHR.sup.5 CHR.sup.6 Y, wherein R.sup.5 and R.sup.6 are, independently, hydrogen, alkyl groups of from one to about eighteen carbon atoms, aryl groups of from six to about eighteen carbon atoms or alkylaryl groups of from seven to about eighteen carbon atoms. Y is a non-acidic group. Related compositions and methods are also disclosed.