Produced water, water that is co-produced during oil and gas manufacturing, represents the largest source of oily wastewaters. Given high oil and gas prices, oil and gas production from non-conventional sources such as tar sands, oil shale and coal bed methane will continue to expand resulting in large quantities of impaired produced water. Treatment of this produced water could improve the economic viability of these oil and gas fields and lead to a new source of water for beneficial use. Two nanofiltration and one low-pressure reverse osmosis membrane have been tested using three produced waters from Colorado, USA. The membranes were analyzed before and after produced water filtration using field emission scanning electron microscopy (FESEM), attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS). In addition, membrane-water contact angles have been measured. XPS data indicate adsorption of organic and inorganic species during filtration. FESEM and ATR-FTIR data support theses findings. Water contact angles indicate the effect of membrane hydrophilicity on fouling. Our results highlight the value of using multiple surface characterization methods with different depths of penetration in order to determine membrane fouling. Depending on the quality of the produced water and the water quality requirements for the beneficial uses being considered, nanofiltration may be a viable process for produced water treatment. (c) 2008 Elsevier B.V. All rights reserved.