The “S-posture” is described in the cetacean literature as a radical flexure of the body which presents an atypically vertical visual signal. It has most commonly been associated with agonistic high arousal contexts, and often includes simultaneous acoustic outbursts. Its dynamic qualities – an abrupt retardation of forward motion, sweeping flexure of the flukes, and sustained arch – suggest its saliency to the cetacean’s motion-sensitive visual system. This study reports on the occurrence of S-postures in four captive beluga whales (Delphinapterus leucas) held at SeaWorld San Diego. During approximately 27 hours of video data, a total of 174 S-postures were displayed by three out of four belugas. None of the S-postures observed co-occurred with another visual display (i.e., bubble clouds, open mouth, jaw clap), while only 8% were observed to have co-occurred with an acoustic production by the whales present. The proportion of S-postures displayed by each subject was analyzed for differences in the following contexts: the state (open/closed) of a rear gate leading to a separate pool, the presence of cohabitant harbor seals (Phoca vitulina), and the total number of belugas in the same pool.