Abstract: A process for the manufacture of an alkyl ester of an aliphatic carboxylic acid comprises the steps of supplying a first feed stream comprising carbon monoxide and an alkene of formula CnH2n to a reactor, supplying a second feed stream comprising an alkyl alcohol, having a formula R—OH where R is an optionally substituted alkyl group, to the reactor, and reacting together said first and second feed streams in the reactor in the presence of a carbonylation catalyst, which catalyses the carbonylation reaction between carbon monoxide and the alkene, to form a product comprising an alkyl alkanoate having the formula CnH2n+1COOR, such that the ratio of alkyl alcohol to alkyl alkanoate present in the reactor is greater than the ratio of alkyl alcohol to alkyl alkanoate present in an azeotropic mixture of the alkyl alcohol and alkyl alkanoate. The process is particularly useful for the manufacture of methyl propionate by the methoxycarbonylation of ethylene.