Proton nuclear magnetic resonance (NMR) measurements have been made to assess the use of NMR in quantifying the pore-scale behavior of hydrocarbon contaminants in porous rocks. NMR measurements were made on bulk water, bulk gasoline (the selected hydrocarbon contaminant), and a sample of Berea sandstone, saturated to various levels with the two fluids. When the sandstone contained either water or gasoline, decreasing the level of fluid saturation resulted in a linear decrease in the total integral of the signal amplitude and in the relaxation time T1. The first effect allows for the determination of the level of fluid saturation from the NMR data; the second effect indicates the preferential drainage of large pores as saturation decreases for both fluids. A significant difference in liquid/rock interaction, which was quantified by calculating the surface sink parameter of the two systems, resulted in separation between the response of the gasoline and the water when the sandstone sample was saturated with a mixture of the two liquids. NMR laboratory measurements proved to be a useful means of detecting and estimating the quantity of a contaminant present in a porous rock. ¿ American Geophysical Union 1993