A method for inhibiting corrosion of pipelines and other metal surfaces, particularly those used in the oil-and-gas industry, is disclosed. The method comprises treating a brine-exposed metal surface with a film-forming composition. The composition comprises a quaternary surfactant, which is made by reacting a polyalkylene glycol (PAG), a haloalkanoic acid, and a tertiary fatty amine that optionally incorporates amide or ester functionality. The surfactant comprises a PAG monoester quat and a PAG diester diquat and may have other components. The quaternary surfactants provide good corrosion protection and can partition effectively from an oily phase into a brine phase in the absence of agitation. The surfactants are easy to synthesize economically and have structures that can be tailored to meet local HLB requirements.