A reactive polymeric surfactant that contains: (a) at least two hydrophilic monomeric units per molecule, each independently according to formula (I): ##STR00001## wherein R.sup.1 is alkylene or oxyalkylene, R.sup.2 is H, methyl, or ethyl, R.sup.3 is H, and n is greater than about 5, (b) one or more hydrophobic monomeric units per molecule, each independently according to formula (II) ##STR00002## wherein R.sup.4 is H or methyl, R.sup.5 is a hydrophobic group, is useful in stabilizing aqueous emulsions and aqueous dispersions.