An analysis of the pilot point method for automated calibration of an ensemble of conditionally simulated transmissivity fields was conducted on the basis of the simplifying assumption that the flow model is a linear function of log transmissivity. The analysis shows that the pilot point and conditional simulation method of model calibration and uncertainty analysis can produce accurate uncertainty measures if it can be assumed that errors of unknown origin in the differences between observed and model-computed water pressures are small. When this assumption is not met, the method could yield significant errors from overparameterization and the neglect of potential sources of model inaccuracy. The conditional simulation part of the method is also shown to be a variant of the percentile bootstrap method, so that when applied to a nonlinear model, the method is subject to bootstrap errors. These sources of error must be considered when using the method. ¿ 2000 American Geophysical Union