Differential scanning calorimetry curves were obtained with aqueous solutions of three alkyldimethylphosphine oxide samples, n-C3DPO, -C9DPO, and -C10DPO, from 293 to 383 K. The heat capacity curves exhibited minimums at 335 +/- 0.5, 329 +/-1, and 321 +/- 4 K, respectively, as do the curves that describe the temperature dependence of the critical micelle concentration (cmc) determined by an independent method. A simple two-state model was used to relate the observed specific heat to the change in heat capacity that accompanies the micelle formation process. The values obtained were used to describe the temperature dependence of the cmc (Desnoyers, J. E.; Caron, G. C.; DeLisi, R.; Roberts, D.; Roux, A.; Perron, G. J. Phys. Chem. 1983, 87, 1397). These results may provide an indication of what to expect for other self-associating systems that lead to micelle formation.