1. Physiological methods applicable to scales between individual leaves and whole forests have the potential to improve substantially our understanding of ecosystem gas exchange. 2. We compared three approaches for determining the canopy gas exchange of individuals representing a pair of mediterranean-climate oak species. 3. We estimated transpiration from the Penman-Monteith equation, measured sap flow with heat-balance sensors, and also measured net CO-2 assimilation, transpiration and conductance with a whole-canopy gas-exchange system. 4. Simultaneously measured sap flow and chamber transpiration were qualitatively similar, provided that the sensors were designed to compensate for thermal gradients along the tree trunk. Both in situ and bench-top measurements indicated that the quantitative relationship beween transpiration and the signal from the sap-flow sensor varied among stems. The sap flow of individual trees measured on consecutive days with the tree in the chamber 1 day, and out the next, was similar, indicating that enclosure had only a small impact on transpiration. Total daily sap flow, which was similar during atmospherically moist period to the Penman-Monteith transpiration calculated assuming a fixed stomatal conductance, became almost insensitive to further increases in evaporative demand during hot and dry intervals. 5. While the application of each approach is limited by experimental considerations, these shortcomings may be overcome by using the techniques in combination.