Pinnipedia, an order of semi-aquatic marine mammals, adapted a body design to locomote both aquatically and terrestrially. The limbs of these amphibious mammals are modified as flippers, which are beneficial for aquatic locomotion, but can limit their locomotion on land. Phocids, like the Northern elephant seal (Mirounga angustirostris), have reduced forelimbs and are unable to bring their hindlimbs beneath them during terrestrial locomotion. Otariids, like the California sea lion (Zalophus californianus), have enlarged forelimbs and can bring their hindlimbs under the body to locomote quadrupedally on land. Due to these differences, phocids are expected to move on land with greater energetic costs compared to otariids. These energetic costs would be exacerbated in large phocids, which use an undulatory, crutching terrestrial gait. The energetic cost of terrestrial locomotion in pinnipeds has only been examined in the elephant seal. To compare the mechanical costs of transport of terrestrial locomotion between otariids and phocids, one male and two female adult California sea lions were video recorded galloping across a runway. From these videos, eight anatomical points of reference were digitized to obtain velocity, amplitude of heave, and frequency of oscillations during the gallop cycle. These variables represent the principal parameters of a biomechanical model that computes the power output of individuals. The model indicates that the quadrupedal gait of otariids has a lower cost of transport than the undulatory gait of phocids.