A continuous process for the co-production of acetic acid and acetic anhydride by (a) contacting carbon monoxide with a liquid reaction composition comprising methyl acetate, dimethyl ether or a mixture thereof, a Group VIII metal catalyst, methyl iodide, acetic acid, acetic anhydride, water in a concentration of 0.1 wt% or less, (b) withdrawing liquid reaction composition from the reaction zone and introducing at least a portion of the withdrawn liquid reaction composition into a flash separation zone, and (c) removing from the flash separation zone a vapour fraction comprising acetic anhydride, acetic acid and methyl iodide and a liquid fraction comprising acetic anhydride, and Group VIII metal catalyst in which at least one of the liquid reaction composition and the withdrawn liquid reaction composition introduced into the flash separation zone comprises at least one metal salt selected from salts of Group IA and Group IIA metals and the molar ratio of acetic acid to acetic anhydride in the vapour fraction removed from the flash separation zone is maintained at greater than or equal to 1, preferably greater than or equal to 1.2.