The unimolecular chemistry of the saturated cations Cn H2n+1(n= 2–12) is examined on the basis that such ions, when produced by electron impact, undergo (in slow reactions) decomposition over the lowest available energy surfaces. There is no evidence for any isolated states which could, in principle, undergo slow reactions (log10K= 4–6) from high energy states. Elimination of neutral molecules (H2, CH4) with σ-bond formation is found for the lower homologues (C2H5+, C3H7+, C4H9+). In higher homologues (C5H11+–C12H25+), only olefin eliminations are observed in slow reactions. With only the assumptions that (a) the various possible olefin eliminations compete one against the other and (b) the reverse reactions (combination of an olefin and a carbenium ion) have zero, or near zero, activation energies, the unimolecular chemistry of the C5-C12 saturated carbenium ions can be either accounted for or predicted.