Abstract: Liquid dyestuffs of the general formula: ##STR1## in which y represents 0 or 1, x and z each represent a whole number in which the sum x + y + z is a whole number from 5 to 17; a process for the preparation of such dyestuffs in which the bis-diazo derivative of bis-(4-amino-phenyl)-sulphide is coupled in aqueous medium with a 2-N-alkylamino-naphthalene of the formula: ##STR2## x, y and z having the same significance as above, in the proportion of two molecules of naphthalene derivative to one molecule of bis-diazo derivative; and the use of these dyestuffs for the coloration of petroleum products, inks, fats, waxes and plastics materials.