Salt carry-over due to excessive foaming in a multistage flash (MSF) distiller and detrimental foaming in the deaerator section have been reported in the Saline Water Conversion Corporation (SWCC) of Saudi Arabia and other desalination plants. The application of a suitable antifoaming agent has prevented distillate contamination and improved release of dissolved oxygen in the deaerator section, thus improving the operating efficiency of MSF plants. The developer of a polyoxypropylene glycol-based antifoaming agent collaborated with SWCC in carrying out trial runs to show that their product was as effective and economical as the one currently being used (a polyglycol blend in a hydrocarbon solvent) in SWCC plants. Trial tests were carried out at laboratory, pilot and commercial plant levels. Miscibility of this agent in water was determined initially in the laboratory, followed by field trial runs in an MSF pilot plant and the commercial plants of Al-Jubail I and II. Foam control, non-interference with antiscalant performance, distillate purity and stability at a low dose rate over a wide range of temperatures were some of the important criteria evaluated during testing of this antifoaming agent. During MSF plant runs, distillate conductivity and dissolved oxygen level in the feed were regularly monitored and found within the acceptable limits. Compatibility of this agent with antiscalant was also assessed. Heat transfer and plant performance data were found satisfactory confirming that this agent did not exhibit any adverse effect on the antiscalant used in Al-Jubail plants. Results of laboratory and field trial runs of this antifoaming agent are discussed.