Results from an analysis of the Southampton Oceanography Centre (SOC) global air–sea heat flux climatology, which has been calculated using in situ weather reports from voluntary observing ships covering the period 1980–93, are presented. Systematic errors in the fluxes arising from differences in observing procedure have been quantified and corrected; the magnitude of these errors is up to 15 W m−2 with strong seasonal and regional variations. Despite these corrections, closure of the ocean heat budget is not obtained as the global mean net heat flux is an oceanic gain of 30 W m−2. The validity of closing the heat budget by global scaling of the flux components is assessed by comparison of the SOC flux fields with Woods Hole Oceanographic Institute research buoy measurements. The level of agreement between the two is found to vary from one site to another. Thus, closure of the ocean heat budget requires regional adjustments to the flux components in order to avoid significant biases in the adjusted fields. Close agreement is found for several buoys deployed in the Subduction Array off the coast of northwest Africa. However, at other buoy deployment sites in the western equatorial Pacific warm pool and south of Bermuda in the North Atlantic, the flux adjustment improves the estimate of the net heat exchange. Further evidence for regional biases is obtained from a comparison of box mean surface heat fluxes derived from hydrographic section data with the corresponding SOC values in the Atlantic and North Pacific. The climatological heat loss is found to be an underestimate in those boxes containing the strongest surface flux expression of the major western boundary currents.