FOLLOWING Salter's1 proposals for the extraction of energy from sea waves, we are working on the prediction of wave power output from devices situated at favourable coastal sites around the UK. While it is hoped that adequate spectral data from sites closer inshore will become available within the next year or so, the best present data for the North-east Atlantic are from O.W.S. India2. We describe here the power available and, on simplified assumptions, the amount that might be extracted by ducks of various diameters. (The Salter 'duck' is a rocking cam-shaped device which is designed to give a high efficiency of energy extraction over a wide frequency band 3.) Confirmation of the validity of the important assumption of additivity of power outputs from wave components of different periods is provided in a separate paper4. © 1976 Nature Publishing Group.