Reapproved March 28, 2000. Supplements API Standard 11AX (6th. ed., 1971) on subsurface pumps and fittings by specifying the material requirements of metallic materials for construction on sucker-rod pumps for service in hydrogen sulfide environments. Recommends materials in tabular form and listed in order of preferred usage for nine environments with varying degrees of abrasion and hydrogen sulfide corrosion. Includes appendices on case hardening processes for steel pump barrels for an H2S environment and selection of optimum type of pump.