We measured esophageal pressures (n = 4), respiratory flow rates (n = 5), and expired O2 and CO2 (n = 4) in five adult Patagonia sea lions (Otaria flavescens, body mass range 94.3-286.0 kg) during voluntary breaths while laying down out of water. The data were used to estimate the dynamic specific lung compliance (sCL), the O2 consumption rate ([Formula: see text]O2) and CO2 production rates ([Formula: see text]CO2) during rest. Our results indicate that the resting tidal volume in Patagonia sea lions is approximately 47-73% of the estimated total lung capacity. The esophageal pressures indicated that expiration is passive during voluntary breaths. The average sCL of sea lions was 0.41 ± 0.11 cmH2O-1, which is similar to those measured in anesthetized sea lions and awake cetaceans, and significantly higher as compared to humans (0.08 cmH2O-1). The average estimated [Formula: see text]O2 and [Formula: see text]CO2 using breath-by-breath respirometry were 1.023 ± 0.327 L O2 min-1 (range: 0.695-1.514 L O2 min-1) and 0.777 ± 0.318 L CO2 min-1, (range: 0.510-1.235 L CO2 min-1), respectively, which is similar to previously published metabolic measurements from California and Steller sea lions using conventional flow-through respirometry. Our data provide end-tidal gas composition and offer novel data for respiratory physiology in pinnipeds, which may be important for clinical medicine and conservation efforts.