An attempt was made to analyze the ultrafiltration characteristics of surfactant (Triton X-100)-oil field brine for a cellulosic membrane. Triton X-100 permeate concentration was found to be invariant with ultrafiltration time and remained below or close to the surfactant critical micelle concentration, suggesting a permeate free of micelles. With an increase of the feed surfactant concentration, the permeate surfactant composition also remained unchanged (~ 1.7 x 104 M) at a feed surfactant concentration of 5 x cmc and 10 x cmc and was slightly above the cmc (2.4 x 104 M) at a feed surfactant concentration 50 times the cmc. This indicates that micelles are completely rejected, which is desirable in micellar-enhanced ultrafiltration (MEUF) applications. The removal of traces of petroleum oil from produced oil field water by micellar- enhanced ultrafiltration was examined using Tergitol XD (block copolymer) surfactant. Excellent oil rejections (~ 99.5%) were achieved in the seldom-explored surfactant concentration regime around the cmc. Unexpected oil rejection (99.6 %) was observed at surfactant concentration moderately below the cmc (0.7 x cmc). This was considered as due to concentration polarization that results in a build-up of surfactant molecules at the solution-membrane interface where micelles are present. These high oil rejections were achieved with an extremely low feed surfactant concentration ( 0.34 mg/L), making the MEUF process economically and environmentally viable. Also the permeate oil concentration was lower than 0.5ppm, satisfying Omani standards for agricultural use. Mixed micelle molar fraction composition SDS(0.8)-XD(0.2), at 10% M total surfactant concentration was selected to remove Mg'* from water solution containing 100 ppm Mg-*. This surfactant concentration is lower than the cmc of the surfactant mixture. Relatively good rejection (53%) of Mgwas achieved with this mixed miceller system.