USDA’s U.S. soybean ending stock forecasts are upwardly biased. To determine the source of this bias, we examine the revision characteristics of the ending stocks forecasts, and examine USDA’s forecasts of other U.S. soybean balance sheet variables and foreign soybean balance sheet variables. Bias in USDA’s soybean export forecasts is the most likely source of ending stock forecast bias. In turn, bias in the U.S. export forecasts has diverse sources, including bias in foreign trade estimates and late in the forecast cycle slow updating of the forecasts to reflect new information.