While harbor porpoises currently enter San Francisco Bay year‐round, evidence suggests a disappearance that spanned approximately 65 yr. The range of energetic costs of basal metabolism, locomotion, thermoregulation, and reproduction was estimated for porpoises, using a velocity‐dependent bioenergetic model to estimate the potential food requirements of this returning predator. The costs of thermoregulation and locomotion varied with velocity while basal metabolism and reproduction did not. The total metabolic rate in W was analyzed for all possible adult reproductive states. Estimated biomass uptake in kg/d for a 68.5 ± 26.5 km daily swimming distance was assessed using a mixed diet of northern anchovy and rockfish for all possible reproductive states and was found to be highest for simultaneously pregnant and lactating females (4.1 ± 1.6 kg/d) and lowest for male porpoises (1.7 ± 0.6 kg/d). Total energy requirements found for harbor porpoises ranged from 79.3 ± 29.0 W to 186.0 ± 58.5 W. The daily energetic intake for lactating porpoises was estimated to be 105% greater than for a nonreproductive female porpoise. Harbor porpoises in SF Bay were found to require approximately 30.4 ± 22.0 metric tons of fish per year from Bay waters.