A previous proportionate mortality ratio analysis revealed elevated mortality from brain tumors, stomach cancer, leukemia, and other cancers among OCAW members employed in three Texas oil refineries. In order to evaluate these findings, complete work histories of cases and a matched set of controls who died from other causes of death were obtained from company personnel records. Work histories were summarized by clasbifying each job title and department entry into one of several broad work categories of refinery unit operations. A worker was considered "exposed" to a work category if he was known to have worked at least 1 day in the category 15 or more years prior to his death. Maximum likelihood estimates of the relative risk for brain tumor, stomach cancer, and leukemia were calculated by work category using a procedure for matched case-control data. No strong associations for brain tumor risk were seen with any work categories. A slight association for leukemia was seen among workers in the Treating category. which included unit operations that reduce the level of aromatic and sulfur constituents of petroleum products and combine them with additives to improve their quality. Stomach cancer risk was elevated among maintenance workers and workers exposed to lubricating oils and paraffin wax processing.