INTRODUCTION The purpose of this revised job classification system is to provide a standardized method for identifying and classifying jobs within the petroleum refining industry@ related petro-chemical operations@ production operations and marketing/transportation. This system is not an API standard@ nor is it intended that companies should adopt the system for internal use. However@ such a system could be utilized in inter- and intra-company occupational health studies whenever job data groupings would be useful. Possible applications include morbidity and mortality studies@ qualitative and quantitative exposure monitoring scheduling@ and medical surveillance scheduling. Thus@ the job classifications must be specific enough to permit meaningful examination of sub-populations within the petroleum industry@ yet broad enough to allow for inter- and intra-company variations@ now and in the past. It was recognized from the outset that most existing job classification systems were devised for administrative purposes; they reflect personnel practices@ organizational structure@ and labor-relations considerations. In these systems@ the factors generally used in classifying jobs are salary@ training or education@ level of responsibility and accountability@ and level of supervision. While useful@ these factors have little bearing on occupational health. In occupational health@ the primary focus is exposure. Since exposure levels can vary with operating conditions@ equipment type@ age and state-of-repair@ it was determined that it was not feasible at this time to differentiate jobs on a quantitative exposure basis. Even qualitatively@ it is difficult to exactly define the work environment because the process streams are often complex mixtures of a large number of chemicals@ and the source of crude and operating parameters may influence their composition. Even though it may not be possible to qualitatively define the work environment@ it is a reasonable assumption that similar processes potentially present similar qualitative exposures. Thus@ process was selected as one variable in classifying a job. The second variable in classifying a job is obviously the job itself. Job titles vary from company to company and are dependent on labor and personnel practices. However@ using functional descriptions of jobs@ a standardized list for the operations was developed.