Ab initio transition-state-theory based master equation methods are used to calculate pressure-dependent rate constants describing cyclopentene consumption. To this end, four potential energy surfaces (C₅H₈ + OH, C₅H₈ + HO₂, C₅H₇, and C₅H₇ + O₂) are characterized at the CCSD(T)-F12/cc-pVDZ-F12//revDSD-PBEP86-D3BJ/def2-TZVPP level of theory. Pressure-dependent rate constants and branching fractions are then determined via 1D master equation calculations. On the OH initiation surface, the rates calculated herein are consistent with recently published experimental rate constants at high temperature, and we elucidate the complex temperature dependence below 800 K, where π-addition becomes prominent. On the HO₂ initiation surface, we find an interesting alternative route to bicyclic ether formation via well-skipping over the HO₂ adduct well. On the cyclopentenyl radical surface, the major product is cyclopentadiene + H. On the cyclopentenyl + O₂ surface, we find that resonance stabilization largely prevents the allylic radical from undergoing oxidation, whereas the alkylic radical has a somewhat elevated propensity for oxidation pathways relative to cyclopentyl