An error analysis of the Global Precipitation Climatology Project emission algorithm is conducted to identify the major error sources of the algorithm and to quantify the estimation biases resulting from these sources. Several error sources are investigated and uncertainties in spatial rainfall rate variability and freezing level height are identified as the most significant. Spatial rainfall rate variability contributes to beam filling error, and beam filling error is investigated in detail by simulation of brightness temperatures resulting from rainfall rate fields with known spatial variabilities. The algorithm is used to estimate rainfall from the simulated brightness temperatures, and the estimation bias is calculated by comparison of the monthly rainfall estimates with the monthly rainfall used to simulate the brightness temperatures. The final result of the study is the mean monthly multiplicative bias error as a function of the freezing level height and the instantaneous rainfall rate variability. ¿ 1998 American Geophysical Union