Measurements of methyl bromide partial pressure and concentration in surface water and air samples in the NW Atlantic Ocean in July 1995 and the Pacific Ocean in October 1995 are presented. Mean atmospheric mixing ratios were found to be 11.4¿0.7 parts per trillion by volume (pptv) for the northern hemisphere and 10.0¿0.5 pptv for the southern hemisphere. Cold, high-latitude water in the Labrador Sea and warm water in the central Pacific were undersaturated in methyl bromide, and some supersaturated waters were found in the Gulf Stream in the Atlantic and around 35 ¿S in the South Pacific. By a simple extrapolation, the global ocean is estimated to be a net sink of 10 (3 to 13) Gg of methyl bromide per year from the atmosphere, with the range including a factor of 2 uncertainty in the piston velocity. ¿ 1998 American Geophysical Union