Models of the tropical Pacific Ocean routinely use bulk formulae to estimate the surface fluxes of heat into and out of the ocean. The formulae generally require atmospheric variables such as cloud cover, surface wind speed, air-sea temperature difference, and relative humidity. Since these quantities are not provided by most tropical Pacific Ocean models, modelers have resorted to simplifying parameterizations in terms of a few primary variables. Several of these parameterizations are tested by using observed data and comparing fluxes calculated using the simplified parameterizations with those from the full bulk formula. The impact of the various parameterizations is also assessed in a tropical Pacific Ocean general circulation model by comparing model sea surface temperature (SST) with the monthly means and anomalies of observed tropical Pacific SST during a 6-year period that included both warm and cold episodes. The different flux parameterizations yield a broad mix of results. Overall, using a constant relative humidity of 0.80 does well, while using a constant downward radiation and a constant air temperature minus SST produces large discrepancies in comparison with the full flux parameterizations. In agreement with previous studies the model runs demonstrate that SST variability on the equator is dominated by wave processes whereas off the equator the surface flux of heat plays a crucial role in determining changes in SST. ¿ American Geophysical Union 1993