The kinetic energy distribution (KERD) determined by Brand et al. [Chem. Phys. 76 (1983) 111] for the iodine loss from energy-selected iodopropane ions has been analyzed by the maximum entropy method. The entropy deficiency DS has been determined and the value of e −DS , which measures the efficiency of phase-space sampling, has been found equal to about 96%, thus corresponding to a nearly fully statistical situation. The phase space theory of Klots describes a slightly more constrained situation with e −DS ≈ 77%. A rapid determination of the sampled fraction of phase space is possible from energy-selected KERDs, based on the fact that there exists a direct relationship between the efficiency e −DS and the reduced maximum of the KERD ϵ red M = ϵ M (E)/〈ϵ〉 E . The product ϵ M (E)P(ϵ M |E) or ϵ red M P(ϵ red M ) holds the same property.