The reaction between acetylenes and carbon monoxide in n-butanol solution in the presence of a palladium iodide/sodium iodide catalyst has been investigated. Acetylene, methyl-, butyl- and phenylacetylene reacted reaoily at atmospheric pressure to yield mixtures of esters. Substituted acrylates, succinates, maleates and fumarates were the major products; the monoesters which were formed were, in the main, non-linear. The effect of various additives on the product spectrum was examined, thus hydrogen chloride enhanced the yield of monoester in most cases, whilst air and other oxidising agents lowered it. Possible mechanistic routes were investigated by isotopic labelling and other techniques. Dimethylacetylene and diphenylacetylene reacted less readily, and it was necessary to employ elevated, pressures to bring about carbonylation. The products then included esters and lactonea.