Martinez discusses and evaluates Weeks' (1965) paper on offshore oil resources and Hubbert's (1962) report on United States oil resources and (1965) reply to a discussion by Ryan (1965). Petroleum resources are the sum total of four different volumes: production, proved reserves, supplementary reserves, and undiscovered reserves. In analyzing oil resources, one should consider that the principal use of the estimates is for long-range planning. The estimates cannot be used as exact parameters, but as guides which provide sound bases to organizations for policy studies and information. Competent researchers should use the Weeks' (1965) method of estimating the magnitude of oil resources and the Hubbert (1965) method of estimating the duration of these resources (modified as necessary by conditioned prediction).