We　use　full-dimensional　classical　trajectories　to　study　how　reaction　probabilities　for　the　D　+　H2　→　DH　+　H　reaction　are　altered　when　the　system　is　confined　to　move　within　various-sized　carbon　nanotubes　(CNTs).　This　study　focuses　on　D　atoms　initially　moving　parallel　to　the　long　axis　of　the　tube.　We　compare　our　results　with　standard　gas-phase　reaction　probabilities.　Enhanced　reaction　probabilities　are　found　for　the　smaller　diameter　CNTs,　and　slight　quenching　is　found　for　the　largest　diameter　CNT　studied.　These　results　are　also　consistent　with　those　of　a　reduced-dimensional,　quantum　study.　The　origins　of　the　confinement　effects　are　discussed　in　terms　of　how　the　CNT　modifies　the　H2　reactant　state　and　of　the　modified　forces　experienced　by　the　incoming　D　atom.　©　2008　American　Chemical　Society.