Transport of nonaqueous phase liquids (NAPLs) in soils is becoming an increasingly serious threat to the environment. Detection and observation of these substances are thus an increasingly important issue. During recent years, studies have used the apparent dielectric constant (Ka) measured by time domain reflectometry (TDR) for determining the saturation of NAPLs (θNAPL) in soils (m3 m-3). Ka has been related to θNAPL using dielectric mixing models. In this approach for the unsaturated zone, the water content θw should be known beforehand (by assumptions or measured using other techniques). Here, unlike previous research, detailed laboratory experiments were conducted to investigate the relationship between the TDR measured Ka and bulk electrical conductivity σa and θNAPL. Calibration was made in homogeneous sand using three different NAPLs. It was shown that the mixing model used previously led to errors up to 0.05 m3 m-3 in saturated sand. Moreover, in unsaturated sand, measurements of Ka only cannot be used for estimation of θNAPL even if θw is known. Instead, TDR's capability of determining both Ka and σa was utilized to estimate θw and θNAPL. The approach presented in this study can be used for simultaneous observation of θw and θNAPL during NAPL transport experiments in both unsaturated and saturated sandy soils. Thus it is potentially helpful when developing new NAPL transport models.