Groundwater contamination by nonaqueous-phase liquids (NAPLs) has become a serious environmental issue. Therefore, it is necessary to estimate the NAPL content (theta(NAPL)) in saturated soil to detect and monitor the NAPL contamination in groundwater. The objective of this study was to investigate three estimation methods for the theta(NAPL) in saturated sandy soil, namely, the noncalibration method (NCM), the permittivity regression method (PRM), and the best-fit alpha method (BF alpha M). These methods utilize the permittivity (K) measured by amplitude domain reflectometry (ADR) and two dielectric mixing models: a theoretical Maxell-de Loor (MD) model and an empirical a model. The NCM applies the measured K to the models directly. The PRM applies the measured K to the models indirectly using the regression equation between the measured and estimated K The RMSEs of the NCM for the alpha model were 0.038 m(3) m(-3) for light NAPL (LNAPL) and 0.015 m(3) m(-3) for dense NAPL (DNAPL) when the constant alpha value was set at 0.5. The RMSEs of the MD model, however, were 0.090 m(3) m(-3) for LNAPL and 0.070 m(3) m(-3) for DNAPL. Using the PRM, the RMSEs of the MID model became much better than those of the NCM. The RMSEs for theta(NAPL) estimated by the BF alpha M were 0.007 m(3) m(-3) for LNAPL and 0.018 m(3) m(-3) for DNAPL. These results demonstrate that theta(NAPL) was estimated easily and with sufficient accuracy with the alpha model and the PRM.