The invention provides a synergistic surfactant composition comprising: (a) a first amphoteric surfactant, which is selected from C8-C22 sultaines, salts thereof, and mixtures thereof; and (b) a second amphoteric surfactant, which is selected from C8-C22 betaines and salts thereof, C8-C22 propionates and salts thereof, and mixtures thereof. This surfactant composition may be used to generate foam that is used for unloading a liquid from a hydrocarbon reservoir. It may be that the liquid unloading of foam generated using the surfactant composition is greater than that of foam generated from the first and second surfactants when they are foamed individually.