An analysis is presented of acoustical transmission measurements which were performed in the oceanic surface duct in two areas of the Pacific Ocean. Three frequencies, three transmitter depths, and three receiver depths were employed. Both areas demonstrated a persistent surface duct but the water mass was more variable in one area than the other. The thermal surveys were inadequate to establish that either area represented the actual thermal front between different water masses. Experimental transmission-loss curves gave good agreement with theoretical curves based upon normal-mode theory. It was not possible to distinguish between the acoustic properties of the two areas either by the experimental transmission-loss data or by an analysis of the observed signal variability.