The employment of multipath time-delay estimation for acoustic source localization with passive autocorrelation and cross-correlation systems is examined. Important differences in multipath time-delay estimation with wideband and narrower band systems are delineated. Several algorithms are presented that convert multipath time-delay estimates into localization quantities, such as source depth or range. Some algorithms presume an isospeed medium, while another employs a procedure using the generic sonar model (GSM) and is applicable to a nonisospeed medium. Examples from a variety of multipath environments are provided that demonstrate consistent improvement in localization performance with the nonisospeed technique over the isospeed algorithms. Also, dramatic improvements are reported at ranges that exhibit a fairly complicated multipath structure. A theoretical comparison of the performance differences as a function of signal-to-noise ratio between a wavefront curvature ranging system and a multipath ranging system is provided. Finally, advantages of combining localization information obtained from wavefront curvature systems and systems which employ multipath time-delay estimation are discussed.