The partial pressure of CO2 (pCO2) was measured at daily and weekly time scales in the waters surrounding mangrove forests in Papua New Guinea, the Bahamas and India. The pCO2 values range from 380 to 4800 ¿atm. These data, together with previously published data, suggest that overall oversaturation of CO2 with respect to atmospheric equilibrium in surface waters is a general feature of mangrove forests, though the entire ecosystems (sediment, water and vegetation) are probably sinks for atmospheric CO2. The computed CO2 fluxes converge to about +50 mmolC m-2 day-1. If this conservative value is extrapolated for worldwide mangrove ecosystems, the global emission of CO2 to the atmosphere is about 50 106 tC year-1. Based on this tentative estimate, mangrove waters appear to be regionally a significant source of CO2 to the atmosphere and should be more thoroughly investigated, especially at seasonal time scale.