A result-oriented medical information system at the Gulf Oil Corporation is described. Mortality data acquired mostly from routine company operations have been used to calculate standardized mortality ratios (SMRs) and life expectancy. Results show that male employees at the age of 20 have a life expectancy of 74.8 years. Compared with the U.S. general population at age 20 with a life expectancy of 71.8 years, Gulf employees have an advantage of exactly three years. Such an advantage may seem small, but it is equivalent to the gain that could be achieved if all deaths from cancer were eliminated in the United States, a hypothetical and impossible situation. These life expectancy data have the potential for use by the company to influence insurance premiums traditionally set by life insurance companies as well as to aid in the management of the company's pension fund. The SMR for all causes for the male employees is 0.82, significantly decreased in comparison with that of the U.S. general population. This favorable experience has been referred to as "the healthy worker effect." Cause-specific SMRs show a generalized pattern of deficits, some of which are statistically significant. None showed a significant increase. Seventy-six percent of the male deaths occurred among employees aged 65 years or older. If these annuitants (those alive at the beginning of the study) were not included and only the active workers were studied, an SMR of only 0.54 would be obtained.(ABSTRACT TRUNCATED AT 250 WORDS)