The study presents the essentials of a method of synthesizing the visibility-weather group elements of marine synoptic reports into a computerized scheme for the purpose of deriving frequencies of marine-fog occurrence. The program, based on an interpretation of reporting guidelines in the Synoptic Code Manual, uses 16 combinations of present and past weather, and visibility, to identify fog in the reports. The program then objectively assigns the duration of fog for the period represented by each of the reports. A prototype climatology of marine-fog occurrence for July, over the North Pacific Ocean, is derived from application of the method to a ten-year data base (1963-72). Results are compared and discussed in relation to other published coastal and marine-fog climatologies. Diurnal fog frequencies at sea and the compatibility of fog observations from Ocean Weather Stations and transient ships are also treated. The continuing work and its goals are described.