In the presence of methanesulfonic acid, the palladium(0)-olefin complexes: [Pd(eta (2)-ol)(P-N)] [ol = dimethyl fumarate or fumaronitrile, P-N = 1-(Ph2P)C6H4-2-CH=NR (R = CMe3 or C6H4OMe-4)] catalyse the alkoxycarbonylation of terminal alkynes. Moderately good rates are obtained when the catalysts are promoted with two equivalents of the free P-N Ligand and a large excess of acid at 120 degreesC. The catalytic data suggest that derivatives of the type [Pd(alkyne)(P-N)(n)] (n = 2-3) are the active catalytic species.