Abstract: A method of carbonylation of formaldehyde is disclosed. In the method, an aqueous formaldehyde concentrate comprising between about 60% by weight and about 85% by weight formaldehyde, carbon monoxide and sulfuric acid are brought together in the absence of an effective amount of added Group IB cocatalyst in a reaction zone under a carbon monoxide partial pressure in the reaction zone of not greater than about 1.72.times.10.sup.7 N/M.sup.2. A carbonylation reaction is thereby effected in which a carbonylation product is produced comprising at least about 2% by weight sulfuric acid and a mixture of compounds of the formula:HO(CH.sub.2 COO).sub.n Hwherein n is a positive integer of at least 1. Also disclosed is a method for preparation of an alkyl glycolate by esterification of the carbonylation reaction mixture.