More than 200,000 km of single-channel and multichannel seismic reflection data are used to construct an isopach map of sediment thickness and a map of depth to basement in the western North Atlantic Ocean basin, including the continental margins of eastern North America. Velocity regression equations and velocity estimates determined statistically from 17 provinces in the basin are used to convert reflection time in the sediments to thickness. 15 degrees N and 45 degrees N lat. and between 40 degrees W and 85 degrees W long., Mercator projection (about 1:4,383,000 at equator). Methods used for map preparation.--Modified journal abstract.