The effect of temperature on the surface tension of soluble and insoluble surfactants was investigated at an air-water interface. Equilibrium surface tension measurements were performed using the Wilhelmy plate technique in which both temperature and concentration were varied systematically. Insoluble surfactants (oleyl alcohol and hemicyanine) and soluble surfactants (Triton X-100 and sodium dodecyl sulfate (SDS)) were used since they are commonly used in hydrodynamic experiments in which the effects of surfactants on free surface dynamics are studied. The principal result of this investigation is that the surface tension of the above-mentioned surfactants decreases linearly with temperature, independent of concentration, with the exception of oleyl alcohol whose surface tension becomes relatively independent of temperature above 23 degrees C. The adequacy of standard models for surfactant behavior in describing these data is considered.