Solvolysis studies of pivaloyl triflate were carried out in the ionic liquid 1-butyl-3-methylimidazolium bistrifluoromethanesulfonamide with various cosolvents. Reaction solutions were analyzed by 1 H NMR and the relative amounts of substitution and elimination products measured. It was found that regardless of cosolvent, increasing the ionic liquid:cosolvent ratio leads to increased elimination product. The rate of increase, however, is dependent on the identity of the cosolvent. Kamlet-Taft solvatochromic parameters of hydrogen bond accepting and donating ability were invoked to explain this phenomenon.