Management of agricultural nonpoint source phosphorus (P) requires identification of fields susceptible to P loss. P-Indices are the most common tools used to identify critical source areas of P loss. However, the success of the P-Index is impeded by insufficient testing against measured P loss data. Due to a shortage of available P loss data sets, simulated data from a quantitative P transport model may be used to test against a P-Index. The objective of this study was to compare predictions from the Texas Best Management Evaluation Tool (TBET) against measured P loss data to determine whether the model can improve P-Indices in the South. Measured P loss data, representing a range of conditions, were used to test TBET on an event-basis. Our results suggest that TBET can generate satisfactory quantitative predictions of runoff, sediment and P loss with site-specific calibration, but may be better suited for parameterization by physiographic region or state.