Abstract: Preparation of high cyclic phosphonitrilic halide, preferably chloride, oligomer mixtures by reaction of phosphorus trichloride, chlorine and ammonia at temperatures from 65.degree. to 180.degree. C. in which the reactants are simultaneously fed to an agitated inert solvent at a rate such that the phosphorus trichloride concentration is at most stoichiometric relative to the chlorine and ammonia concentration and such that petroleum ether insoluble phosphonitrilic chloride formation is suppressed, and recovering the cyclic phosphonitrilic halide oligomer mixture without extracting petroleum ether insoluble materials since these are not produced.