Disclosed is a hydrocarboxylation process for the production of carboxylic acid from olefins wherein an olefin, water, a Group VIII metal hydrocarboxylation catalyst, an onium salt compound are combined in a reaction zone and contacted with carbon monoxide under hydrocarboxylation conditions of pressure and temperature The process does not require or utilize the addition of a hydrogen halide or an alkyl halide exogenous or extraneous to the hydrocarboxylation process.