In this research, hydraulic and sorption behavior of geosynthetic clay liners (GCLs) with ordinary and modified clay exposed to crude oil were studied. Both modified and ordinary bentonites were investigated to evaluate crude oil adsorption efficiency on the liners. Because soil permeability exposed to crude oil is a major parameter in measuring the contaminants migration in soils, the permeability tests were conducted on the clays. X-ray diffraction (XRD) analyses were also carried out to evaluate the adsorption of crude oil by bentonites. Following the tests, results of XRD analysis for modified bentonite samples indicated an average 63.2% interlayer increase after their exposure to the crude oil while that of ordinary bentonite was relatively insignificant (0.5%). In case of permeability tests, modified bentonites showed much lower permeability values (5.2 × 10^-9 cm/s) compared to ordinary bentonites (1.2 × 10^-6 cm/s) when exposed to crude oil, hence denoting the viability of modified clays, instead of ordinary clays as GCLs materials at petroleum contaminated sites.