The Puerto Rico-Virgin Islands carbonate platform was deposited over an area of 18,000 km2 from early Oligocene to Holocene on top of an inactive and subsiding Cretaceous-earliest Oligocene island arc. Regional single-channel and multichannel seismic reflection lines presented in this study provide the first information on the regional stratigraphy and structure of this platform that has previously been known mainly from onshore stratigraphic sections of a relatively small (2250 km2) portion of the platform exposed by late Neogene tectonic uplift along the north coast of Puerto Rico. Seismic reflection lines are used to map the thickness of the carbonate platform strata and to correlate this thickness with onshore outcrop and well data from northern and southern Puerto Rico, St. Croix (U.S. Virgin Islands), and the Saba Bank. Limestone thickness variations from a little over 2 km to almost zero are used to subdivide the Puerto Rico-Virgin Islands platform into five distinct carbonate provinces: (1) north Puerto Rico area including the onshore exposures; (2) Virgin Islands area; (3) St. Croix and Saba Bank area; (4) south Puerto Rico area; and (5) Mona Passage area. Carbonate thickness and structural information from each area are used to test five previously proposed models for the deformation and vertical movements of the platform. The most prominent feature of the platform in the Puerto Rico-Virgin Islands area is a large, east-west trending arch. The northern limb of this arch exhibits a smoother, more uniform dip than the steeper, more abruptly faulted, southern limb. The core of the arch is responsible for the exposure of arc basement rocks on Puerto Rico. The origin of this arch, which occurs over a 300 km wide area, is best explained by north-south shortening and arching, caused by interaction at depth of subducted slabs of the North America and Caribbean plates. Other important evidence for this model can be found in the Benioff zones observed in the earthquake profiles. Loading of the Caribbean plate results in downward flexing of the North America plate and causes the 4 km subsidence of the carbonate platform north of Puerto Rico. ¿ 1998 American Geophysical Union