One of the major challenges encountered when localizing multiple speakers in real world environments is the need to overcome the effect of multipath distortion due to room reverberation. A wide range of methods has been proposed for speaker localization, many based on microphone array processing. Some of these methods are designed for the localization of coherent sources, typical of multipath environments, and some have even reported limited robustness to reverberation. Nevertheless, speaker localization under conditions of high reverberation still remains a challenging task. This paper proposes a novel multiple-speaker localization technique suitable for environments with high reverberation, based on a spherical microphone array and processing in the spherical harmonics (SH) domain. The non-stationarity and sparsity of speech, as well as frequency smoothing in the SH domain, are exploited in the development of a direct-path dominance test. This test can identify time-frequency (TF) bins that contain contributions from only one significant source and no significant contribution from room reflections, such that localization based on these selected TF-bins is performed accurately, avoiding the potential distortion due to other sources and reverberation. Computer simulations and an experiment in a real reverberant room validate the robustness of the proposed method in the presence of high reverberation .