Rates for the dihydrogen elimination of methane, ethane, and propane with cationic platinum clusters Ptn+ (1 ≤ n ≤ 21) were measured under single collision conditions in a Fourier transform ion cyclotron resonance mass spectrometer (FT-ICR). The reaction rate for a given cluster, Ptn+, increases regularly along the series k(CH4) < k(C2H6) < k(C3H8). Methane is particular in the sense that reactivity is highly variable; some clusters (n = 1 – 3, 5 – 9, 11, 12, 15) are very reactive towards methane, while all other clusters react with low efficiency. For propane all clusters react efficiently, while the reactivity of ethane lays in-between that of methane and propane. By necessity, dihydrogen elimination of methane occurs according to a 1,1-elimination mechanism. Ethane dehydrogenation takes place according to both a 1,1- and a 1,2-mechanism. The difference between the 1,1- and 1,2-mechanisms is well displayed in specifically increased rates for those clusters that were inefficient in the reaction with methane, as well as in the observed selectivity for H2, HD, and D2 elimination in the reaction with ethane-1,1,1-d3. Some twofold dihydrogen elimination is observed as well. The outcome of reactions with C2H6 in the presence of D2 demonstrates the reversibility of dehydrogenation by exchanging all hydrogen atoms in PtnC2H4+ with deuterium atoms. A potential energy diagram with a high barrier for the second H2-elimination summarizes these observations. For propane twofold dihydrogen elimination is dominating, and for these reactions a far less regiospecific and more random loss of the hydrogens can be inferred, as was demonstrated by the reactions with propane-1,1,1,3,3,3-d6.