We have used the differential capillary-rise and the pendant-drop methods to determine the surface tension of aqueous solutions of diethanolamine (DEA), as a function of concentration, in the range 293-363 K and aqueous solution of methyldiethanolamine (MDEA), as a function of concentration, at 323.15 K. We have also studied aqueous blends of MDEA and DEA in the range 313-333 K, at a total concentration of the two amines of 50 mass%, using different MDEA/DEA mass ratios. Furthermore, since foaming is a surface phenomenon that is present in absorption equipment it has to be studied in order to develop sound mitigation techniques through the use of foam inhibitors, thus the surface tension of aqueous DEA (20 mass%) has also been studied with the nonionic surfactants Span20, Span80, and Brij92, at different temperatures, as a function of concentration around their critical micelle concentration (CMC).