"Introduction This is the fourth report on environmental protection expenditures of the petroleum industry within the United States prepared by the American Petroleum Institute's Division of Environmental Affairs. The first report covered actual expenditures for 1966 and 1967@ and estimated expenditures for 1968. The second and third reports each added two additional years of data. This report summarizes all previous reports and adds data for 1973. The same general format was used for each of the four surveys so that the annual expenditures for each reporting period could be compared with previous annual expenditures. It should be noted that each of the four studies has had a slightly different reporting base@ because the number of cooperating companies varied from survey to survey. The ""totals"" reported here are the sums of the expenditures reported to API rather than the total expenditures of the industry. The partial expenditures have not been extrapolated to represent 100 per cent of the expenditures. It will be noted that expenditures in the category of ""Land and Other"" were only reported starting in 1970. A facsimile of the questionnaire used in the survey is found in the back of this report. These questionnaires were submitted to the corporate offices of the member companies of API and to members of the National Petroleum Refiners Association. The companies participating in the survey had the capability to process 13@843@887 barrels of crude oil each day in 1973. This is equivalent to 88.9 per cent of the total 1973 industry refining capacity in accordance with the tabulation contained in the April 1974 ""Oil and Gas Journal."" The companies which have participated in this survey series have reported environmental expenditures for the period of 1956 through 1973 totalling $5.5 billion."