Abstract The production rate in the Coalinga plant averaged 4300 gallons per day (gpd) to December 31, 1965, and 5,000 gpd (50° recovery) in the first nine months of 1966, with a salt content during the 16 months period of 200–350 ppm. The plant has been on stream 98 1 2 percent of the time, a record primarily attributable to the dependability of the tubular assemblies and the ready replaceability of any assembly, without disturbing neighboring assemblies, and without complete plant shutdown. In 1965, several steep declines in production rate occurred due to deposition of ferric hydroxide, probably produced in situ on the surface of the membrane by the reaction of ferrous ion with dissolved oxygen. Starting in November 1965, continuous feed brine dosing with sodium sulfite eliminated dissolved oxygen and arrested steep production declines. In July 1966 a different antifouling method was initiated. Since then the membrane tubes have been scrubbed in-place every 3–4 days by passing a foam ball through the array. For membranes so cleaned, a desalinized water flux rate of small amplitude can be maintained subsequent to any initial decline from this range due to membrane substructure compaction. After sixteen months of plant operation, a majority of the tubes had accumulated at least nine months adequate service, and twelve tubes had accumulated about 14 months. Experience with this plant seems to indicate that acid pretreatment of natural brines, which has been recommended by other investigators, may not be necessary to obtain adequate membrane life, which is conservatively estimated at one year.