Engine lubricating oils require the presence of additives to protect the engine from wear. For almost forty years, the principal antiwear additive for engine lubricating oils has been zinc dialkyldithiophosphate (ZDDP). However, ZDDP must be used in concentrations of 1.4 wt. % or greater to be effective.
Pennzoil Platinum contains 3.00% of Zinc alkyl dithiophosphate (ester).
I use Pennzoil Platinum 5w-30 and highly recommend it.
http://www.epc.shell.com/Docs/GSAP_msds_00018715.PDF
Lubricating oil containing an alkyl alkoxyalkylxanthate and zinc dialkyldithiophosphate - US Patent 5026492 Description