The measurement of specific surface area of porous materials has long been important in physical sciences and iscurrently growing in importance in applied and environmental science. Numerous systems have been developed forsurface area measurement by gas adsorption. Commercial systems are available which can measure a wide range ofabsolute surface area with relative ease. However, their cost is often prohibitive. In this study, an inexpensive apparatusfor surface area measurement has been set up to be used for measuring supercritical adsorption of CO2. The Ono-KondoLattice model was used to represent the adsorption isotherm and to determine the surface area. The results of surfacearea determination using CO2 adsorption combined with OK model have been compared to the numbers obtained fromnitrogen BET method. For surface area determination of zeolites and activated carbons, the new method give reasonableagreement results (within 10% deviation) compared to the results obtained from nitrogen BET method. In addition, thenew method also gives more reasonable results for surface area determination of coals. As known, the nitrogen BETmethod gives almost zero of coals’ surface area. This might due to the characteristic of the coals’ structure that might bechange (the pores are closed) during the cooling process in nitrogen BET method. Moreover, the new method can alsobe used to determine the surface area of porous materials using CO2 adsorption data at various temperatures withoutsacrificing their accuracy.