The deceleration patterns following a leap by the calanoid copepod, Labidocera trispinosa were used to determine the parameters k and n in the proposed drag law Cd =k(Re)−n where Cd is the drag coefficient and Re is the Reynolds number. This relation was used to calculate the rate of energy expenditure in constant velocity swimming and in accelerating from rest to a given velocity. At the velocities and accelerations observed, assuming 100% metabolic and propulsive efficiency, the rate of energy expenditure is slightly greater than 0.1% of the basal metabolic rate. It was also shown that at the swimming speeds observed during vertical migrations, the rate of energy expenditure is slightly less than 0.3% of the basal metabolic rate.