The reactivity of two bicyclic alkenes, bicyclo[2.2.2]octene (BOE) and norbornene (NBE), has been studied on Pt(111) in both the absence and the presence of co-adsorbed hydrogen. The inability of these alkenes to rearrange to alkylidyne species on the surface considerably alters their reaction chemistry. At 130 K, the alkenes are bound molecularly to the surface via two interactions : (1) a pi or di-sigma interaction with a C=C double bond, and (2) an apparent agostic interaction with a C-H bond. The geometries of these bicyclic alkenes strongly suggest that they are interacting with three mutually-adjacent surface Pt atoms, but it is not clear from the data whether the alkene group bridges between two Pt atoms and the agostic interaction involves one Pt atom or vice versa. Several reactions ensue upon thermolysis. At similar to 250 K, the agostic C-H bond is cleaved and a surface-bound alkyl intermediate is formed. The resulting surface-bound hydrogen atoms do not immediately desorb, but some of them transfer to unreacted BOE and NBE molecules to form the alkanes bicyclo[2.2.2]octane (BOA) and norbornane (NEA), respectively. The rate-determining step for this self-hydrogenation reaction is the dehydrogenation of BOE or NBE; these processes appear to follow first-order rate laws with activation energies of similar to 16 kcal/mol. : (1) a pi or di-sigma interaction with a C=C double bond, and (2) an apparent agostic interaction with a C-H bond. The geometries of these bicyclic alkenes strongly suggest that they are interacting with three mutually-adjacent surface Pt atoms, but it is not clear from the data whether the alkene group bridges between two Pt atoms and the agostic interaction involves one Pt atom or vice versa. Several reactions ensue upon thermolysis. At similar to 250 K, the agostic C-H bond is cleaved and a surface-bound alkyl intermediate is formed. The resulting surface-bound hydrogen atoms do not immediately desorb, but some of them transfer to unreacted BOE and NBE molecules to form the alkanes bicyclo[2.2.2]octane (BOA) and norbornane (NEA), respectively. The rate-determining step for this self-hydrogenation reaction is the dehydrogenation of BOE or NBE; these processes appear to follow first-order rate laws with activation energies of similar to 16 kcal/mol.