The Ostwald concentration coefficients of acetonitrile in aqueous methanol, propan-1-ol, 2-methylpropan-2-ol (tert-butyl alcohol), 1,4-dioxane, and dimethyl sulfoxide have been measured by determining the acetonitrile concentrations in the liquid and vapor phases by gas chromatography. The method described is self-calibrating and allows the rapid determination of gas solubilities. It is found that the acetonitrile solubility varies nonlinearly, and nonmonotonically, in the mixed solvents, passing through maxima in the aqueous alcohol and 1,4-dioxane systems and showing a shallow minimum in the aqueous dimethyl sulfoxide mixtures.