The EP films generated by borate-containing lubricants were studied to determine their structure and mode of action. Films were generated on SAE Machine test specimens with a blend of tribenzyl borate in solvent neutral oil. Study of the generated films in situ and after chemical stripping show them to be amorphous structures a few thousand angstroms thick containing boron, ferrous iron and organic components. Attempts to reproduce film material synthetically are described. Surfaces with borate EP films are shown to be harder than the steel substrate. Thus, they do not conform to the usual concept of more conventional EP agents which are generally believed to provide an easily-sheared film.Presented as an American Society of Lubrication Engineers paper at the Lubrication Conference held in Minneapolis Minnesota, October 18–20, 1966.