Adsorption of nitromethane on oxide surfaces was monitored using C-13 CP/MAS NMR. Stabilization of the aci-anion formed by reaction of nitromethane on acid-base pairs was apparent. A linear relationship between the C-13 NMR isotropic chemical shift of the methylene group of the adsorbed aci-anion of nitromethane and the heat of adsorption Of CO2 measured by microcalorimetry was established. The results suggest that nitromethane constitutes an accurate and effective NMR probe for monitoring the basicity of oxide surfaces.