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The reaction mechanism of the gas-phase Pt atom with C<sub>3</sub>H<sub>8</sub> has been systematically investigated on the singlet and triplet potential energy surfaces at CCSD(T)//BPW91/6-311++G(d, p), Lanl2dz level. Pt atom prefers the attack of primary over secondary C-H bonds in propane. For the Pt + C<sub>3</sub>H<sub>8</sub> reaction, the major and minor reaction channels lead to PtC<sub>3</sub>H<sub>6</sub> + H<sub>2</sub> and PtCH<sub>2</sub> + C<sub>2</sub>H<sub>6</sub>, respectively, whereas the possibility to form products PtC<sub>2</sub>H<sub>4</sub> + CH<sub>4</sub> is so small that it can be neglected. The minimal energy reaction pathway for the formation of PtC<sub>3</sub>H<sub>6</sub> + H<sub>2</sub>, involving one spin inversion, prefers to start at the triplet state and afterward proceed along the singlet state. The optimal C-C bond cleavages are assigned to C-H bond activation as the first step, followed by cleavage of a C-C bond. The C-H insertion intermediates are kinetically favored over the C-C insertion intermediates. From C-C to C-H oxidative insertion, the lowering of activation barrier is mainly caused by the more stabilizing transition state interaction Δ<em>E</em><sup>≠</sup><sub>int</sub>, which is the actual interaction energy between the deformed reactants in the transition state.