Beginning with a detailed mechanism of 176 reversible elementary steps among 37 species, reduced mechanisms are derived for predicting autoignition times at temperatures between 1000 K and 2000 K, pressures between 1 bar and 100 bar, and equivalence ratios between 0.5 and 2.0, for C3H8/ air, C3H6/ air and C3H4/ air mixtures. Short mechanisms for allene and propyne of 23 irreversible steps among 19 species, for propene of 32 irreversible steps among 21 species, and for propane of 40 irreversible steps among 25 species are shown to yield ignition times in very good agreement with those of the detailed mechanism. By taking into account chemical-kinetic steady states, these mechanisms are reduced to 16 steps among 14 species for C3H4, 25 steps among 17 species for C3H6, and 23 steps among 17 species for C3H8. The procedures that would have to be followed to achieve further systematic reductions of these mechanisms are indicated. The results can be of help in calculating autoignition of these fuels in detonations and in HCCI engines.