Carbonylation of alkynes has been carried out using a catalyst system consisting of Pd(OAc)(2), a monophosphine, p-toluene sulphonic acid and semilabile anionic bidentate ligands such as pyridine or piperidine carboxylic acids. Turnover frequencies (TOF) upto 3500 h(-1) and 98% selectivity to 2-substituted 2-propenoic acid/ester have been achieved under mild CO pressures of 1-3 atm at 373 K.