Abstract: Additives made by reaction of (A) at least one phosphorus acid compound of the formula: ##STR1## wherein each X is independently oxygen or divalent sulfur, M is hydrogen or an equivalent of metal or ammonium cation, R is a hydrogen atom or a hydrocarbyl or hydrocarbyloxy or hydrocarbyl mercapto group of about one to about thirty carbon atoms and R' is XM or R with the proviso that the total number of carbon atoms in both R and R' is at least two, with (B) at least one sulfo-containing compound of the formulae: ##STR2## wherein y is one or two, R.sup.3 is hydrogen or lower alkyl group, R.sup.2 is a divalent or trivalent hydrocarbyl group, R.sup.4 is a trivalent hydrocarbyl group, and Q is --OH, --OR.sup.3, --OM, an alkylene polyamine residue, or N(R.sub.3).sub.2, are novel and useful and have utility as, for example, additives for water-containing hydraulic fluids.