Measurements of the distribution of CO b2s between the atmosphere and the sea are presented with a description of the apparatus used and its calibration. The measurements were made on a series of cruises into the Gulf of Mexico, the Northern Caribbean Sea and the Western North Atlantic Ocean, in the gas phase using a nondispersive double-beam infrared analyzer. Four geographical patterns in the distribution of COb2s between the phases were observed; first, pCOb2s of the air over the Southwestern Gulf of Mexico, the Gulf of Campeche and a 40 mile wide strip near shore of the Louisiana Gulf Coast was 303 ppm and pCOb2s of the surface waters was 270-290 ppm. The second, bounded by the Bahama Banks, the island of Bermuda and the continental United States, has a pCO b2s of 311 to 312 ppm in the air and PCOb2s of the waters was 290 ppm. A diurnal cycle in pCOb2s of the air of 4-8 ppm was observed over this area. The maximum occurred at 1800 hours local time and the minimum between 2400 and 0600. The third, consisting of the Northern Caribbean and Atlantic south of the Bahama Banks, where pCOb2s of the air was 316 ppm and pCOb2s of the surface waters was between 270 and 300 ppm. A tropical rain squall in this area produced large excursions to 330 ppm of pCOb2s in the sea to a depth of 200 feet. The fourth, the Eastern Gulf of Mexico from the straits of Florida to the mouth of the Mississippi River, pCOb2s in the air averaged 316 ppm and pCOb2s of the sea was above 325 ppm. A diurnal cycle of 70 ppm in the pCOb2s of the sea was observed in the Gulf of Batabano, Cuba, the maximum was 400 ppm at the time of maximum insolation and the minimum occurred before dawn. The change in pCOb2s per degree centigrade in sea water of 19% chlorinity and pH of 8.2 was measured and is a 4.5 ppm. The change in pCOb2s with temperature is a function of pH and for the same water is 7. 0 ppm per degree at pH of 8.0.