Wind speed data in the atmospheric boundary layer (ABL) observed during two recent experiments over a wide stability range and over different experimental areas allowed an extensive test of the ABL bulk similarity equation with the similarity functions Bw previously proposed and calibrated with the First International Satellite Land Surface Climatology Project (ISLSCP) Field Experiment (FIFE) data set in order to obtain regional surface momentum fluxes. It was found that FIFE-calibrated Bw functions produced similarly good results with the two new data sets; furthermore, one similarity function Bw based on a simple dual-layer ABL model which worked best with the FIFE data set was also found to perform best with the new data sets. Recalibration of the constant of this Bw function with all three combined data sets resulted in the same value as that calibrated with the FIFE data set. ¿ 1999 American Geophysical Union