Kinetic and product ratio studies are consistent with the following mechanisms for the hydrolysis of methanesulfonyl chloride: (a) in acidic medium (pH 1–6) via a direct substitution on sulfur (SN2-S), (b)in mildly basic medium (pH 8–10) by way of sulfene (CH2=SO2) formation followed by trapping with water, and (c) in strongly basic solution (pH > 10) via sulfene with trapping by the hydroxide ion. The reactions of primary and secondary alkanesulfonyl chlorides are qualitatively similar.