Isothermal adsorption data for n-butane and isobutane on BAX 1500 activated carbon reported by Whittaker et al. [Whittaker, P. B.; Wang, X.; Zimmermann, W.; Regenauer-Lieb, K.; Chua, H. T. Predicting the Integral Heat of Adsorption for Gas Physisorption on Microporous and Mesoporous Adsorbents. J. Phys. Chem. C 2014, 118 (16), 8350-8358, DOI:] were modeled with pressure-varying Langmuir adsorption parameters using flexible least squares for pressure-varying linear regression. Coverage varies with pressure and at distinct transitions; when the ratio of uptake to capacity is 0.69 +/- 0.04, monolayer coverage is achieved or micropore volume is filled. Monolayer transitions are observed for the 298, 323, and 348 K isotherms, while micropore volume transitions are only apparent for the 298 K isotherms. The resultant adsorbent surface area is 1335 +/- 25 cm(2) g(-1), and the micropore volume is 0.48 +/- 0.03 cm(3) g(-1). Molecular areas, corresponding to excluded adsorbate areas, are dependent upon the temperature and range from 29.1 to 31.1 angstrom(2) for n-butane and from 31.8 to 32.7 angstrom(2) for isobutane for the 298-348 K isotherms. Average molecular areas, calculated from monolayer capacities, are 20.5 +/- 0.4 angstrom(2) for n-butane and 21.9 +/- 0.7 angstrom(2) for isobutane and correspond to minimum areas, excluding surface mobility and packing. Molecular volumes, calculated from micropore volume capacities, are 45 +/- 2 angstrom(3) for n-butane and 58 +/- 2 angstrom(3) for isobutane and are comparable to molecular volumes determined from Lennard-Jones 12:6 potentials. Entropies of adsorption increase from -1.06 +/- 0.04 kJ K-1 kg(-1) at 298 K to -0.671 +/- 0.008 kJ K-1 kg(-1) at 348 K for n-butane and from -0.948 +/- 0.018 kJ K-1 kg(-1) at 298 K to -0.682 +/- 0.010 kJ K-1 kg(-1) at 348 K for isobutane and indicate increased mobility at monolayer coverage.