This study, investigates the feasibility Of Using ethylene oxide (EO) chain adsorption to determine the surface area of smectite in water. Experimental results indicate that high-molecular-weight poly(ethylene oxide) (PEO) should be used to provide reasonable estimations for monolayer capacity of PEO oil smectite. The surface areas of smectites in water are calculated from the monolayer capacity of PEO adsorbed oil smectite by taking the area per EO unit as 8.05 angstrom(2). The method measures the actual surface area of smectite exposed when dispersed in water. which is important to applications Of smectite Under aqueous conditions. (c) 2004 Elsevier Inc. All rights reserved.