This paper summarizes some previously unpublished recreational boat usage and boat performance information which has been sponsored or obtained by marine engine manufacturers. It describes how this information was used to develop the international ICOMIA Standard No. 36-88, Marine Engine Duty Cycle, published by the International Council of Marine Industry Associations. The boat usage information includes some historic data obtained by the Boating Industry Association, Outboard Marine Corporation, and Mercury Marine. The data obtained by the BIA were analyzed and summarized by the University of Wisconsin, Madison.Also included is the reasoning which led to the concept of Marine Engine Efficiency Index. This is a simple modification of the specific fuel consumption and approximates the influence of engine weight and typical fuel load on recreational boat performance.