N-methyl-N-acylglucamines are suitable as thickening agents in aqueous surfactant solutions containing one or more anionic surfactants of the group including alkyl ether sulfates and alkyl sulfates, the N-methyl-N-acylglucamines containing at least 60 wt.-% of N-methyl-N-acylglucamines that have a C12-, C14-acyl group or an unsaturated C18-acyl group and at the same time less than 5 wt.-% of N-methyl-N-acylglucamines that contain an acyl group
