This paper is part of a series designed to examine the trophic and energy relationships of large decapod crustaceans. The oxygen consumption and daily energy loss due to respiration were measured in the California spiny lobster, Panulirus interruptus. At 13°, 16°, and 20° C, the QO2 was 0.0339, 0.0483, and 0.0655 ml/g wet body weight/hr, respectively, for individuals weighing between 200 and 600 g. Within this weight range QO2 was independent of body weight but was dependent on temperature, yielding a Q10 estimate of 3.25 from 13°-16° C and a corresponding coefficient of 2.14 from 16°-20° C. The QO2 of this species is fairly similar to that of other palinurid and homarid lobsters and somewhat lower than those of several crab species. P. interruptus is an oxygen regulator, with Pc located between 25 and 45% air saturation.