In the production of washing-active .alpha.-sulfofatty acid esters by sulfonation of fatty acid alkyl esters with SO.sub.3 in molar ratios of up to 1:2 and more especially of from 1:1.2 to 1:1.8 and subsequent working-up of the crude sulfonic acid in aqueous medium with salt formation, aqueous pastes which are mobile, more especially pumpable, at moderately elevated temperatures are obtained by subjecting the crude sulfonate before the treatment with the aqueous medium to a post-reaction with at least about 0.5 mole equivalent, based on the SO.sub.3 which is not used for the .alpha.-sulfonation, of monohydric alcohols and/or alkoxylation products thereof at temperatures above 70.degree. C. and adjusting the solids contents of the .alpha.-sulfofatty acid ester salts to more than 35% by weight in the subsequent aqueous working-up step.