Excised lungs from 8 marine mammal species (harp Pagophilus groenlandicus,harbor Phoca vitulina, and gray seal Halichoerus grypus, Atlantic white-sidedLagenorhynchus acutus, common Delphinus delphis and Risso's dolphin Grampus griseus,long finned pilot whale Globicephala melas, and harbor porpoise Phocoena phocoena) wereused to determine minimum air volume of the relaxed lung (MAV, n = 15) and the elasticproperties (pressure-volume curves, n = 24) of the respiratory system, and total lung capacity(TLC). Our data indicate that mass-specific TLC (sTLC, l • kg-1) does not differ between speciesor groups (odontocete vs. phocid) and agree with that estimated (TLCest) from body mass (Mb)by: TLCest = 0.135 • Mb0.92. Measured MAV was on average 7% of TLC, with a range from 0%to 16%. The pressure-volume curves were similar among species on inflation but divergedduring deflation in phocids as compared with odontocetes. These differences provide a structuralbasis for observed species differences in depth at which lungs collapse and gas exchange ceases. Author Posting. © The Author(s), 2011. This is the author's version of the work. It is posted here by permission of The Company of Biologists for personal use, not for redistribution. The definitive version was published in Journal of Experimental Biology 214 (2011): 3822-3828, doi:10.1242/jeb.056366. This project was supported by a grant from the Office of NavalResearch (ONR award number N00014-10-1-0059; Dr. Loring was supported by HL 52586 fromthe National Institutes of Health.