During terrestrial locomotion, frogs use two distinct gaits: out-of-phase leg movements associated with slow crawling behaviour and in-phase leg movements during fast jumps. In Rana esculenta, crawling occurs during feeding, while jumping is used as an escape strategy. We examined whether a similar velocity-dependent gait shift appears in swimming R. esculenta. Typically, swimming frogs propel themselves by kicking both hind limbs simultaneously. Observations of out-of-phase leg movements in swimming frogs have been reported, but were usually assumed to be associated only with directional changes. We demonstrate that alternating-leg swimming is used quite frequently and that it results in a significantly lower velocity to the one obtained by using in-phase leg movements. This difference is likely to be associated with energetic costs. Mathematical estimates of positive mechanical work required to move the centre of mass revealed that out-of-phase swimming is energetically less expensive than the in-phase gait at a comparable speed, but may not be efficient at high speeds. Possible explanations for this phenomenon are higher inertial energy losses for in-phase swimming, but at high speeds jet propulsion and an interaction effect may gain importance.