The authors performed ball-on-disk and four-ball tests. The former gave much less severe conditions than the latter. A ZDDP-containing package, blended with a mineral base oil, was tested. Completely different mechanisms of ZDDP conversions were observed. During ball-on-disk tests, ZDDP undergoes partial tribochemical decomposition. It results in a modification of the surface of test specimens—organic compounds are produced and zinc atoms diffuse into the surface. During four-ball tests, advanced structural decomposition of ZDDP takes place—S and P take part in tribochemical reactions. Probably inorganic compounds are produced, whereas there is a lack of a layer of organic ones adsorbed on the surface. The generation of inorganic compounds results from chemical reactions of decomposed ZDDP with the surface of steel specimens as well as diffusion of some elements (e.g. S) into the surface. Good antiseizure properties of such inorganic structures help to improve the tribological characteristics under severe test conditions.