Continuous measurements of atmospheric CO₂ concentrations made at various heights within and above a mature oil palm canopy showed that concentrations varied widely during the course of a 24-hour period – building up to high levels overnight within the canopy and falling rapidly with the onset of photosynthesis in the morning. Measurement of CO₂ fluxes, both within the atmospheric boundary layer above the canopy and within the trunk space, allowed the relative contribution of CO₂ supplied from the above and below-canopy atmosphere to the total canopy CO₂ assimilation to be assessed. Similar assessment of water vapour fluxes provided a measure of the percentage of water lost as evapotranspiration (ET) which was channelled through the palms. Below-canopy CO₂ uptake averaged 18.5% of the above-canopy flux and 15.6% to total flux. Evapotranspiration from the ground (from soil and ground flora) was almost 13% of total evapotranspiration, so that over 87% of ET took place directly from the palm canopy.