Alkylaryl- and alkylpolyethylenoxy phosphate ester acids and their salts were found to be effective load-carrying and rust-inhibiting additives for metalworking fluids. Falex and four-ball data showed that performance in oil, emulsion, and water systems were dependent upon the hydrophobe type and ethylene oxide content. Chip tests demonstrated that chemical composition also influenced rust inhibition.Contributed by the ASLE Fluids for Metalworking Committee and presented at the Annual Meeting of the American Society of Lubrication Engineers held in Chicago, Illinois, May, 1964.