The production of HO2 from the reaction of c-C5H9 + O-2 has been investigated as a function of temperature (296-723 K) by using laser photolysis/CW infrared frequency modulation spectroscopy. The HO2 yield is derived by comparison with the Cl-2/CH3OH/O-2 system and is corrected to account for HO2 signal loss due to competing reactions involving HO2 radical and the adduct c-C5H9O2 The time behavior of the HO2 signal following cyclopentyl radical formation displays two separate components. The first component is a prompt production of HO2, which increases with temperature and is the only component observed between 296 and 500 K. The yield from the prompt production rises from less than 1% at 296 K to similar to 23% at 693 K. At temperatures above 500 K a second slower rise in the HO2 signal is also observed. The production of HO2 on a slower time scale is attributable to cyclopentylperoxy radical decomposition. The total HO2 yield, including the contribution from the slower rise, increases dramatically with temperature from similar to2% at 500 K to similar to 100% at 683 K. From 683 to 723 K the total HO2 yield remains constant. The second slower rise accounts for a majority of the product formation at these higher temperatures. The biexponential time behavior of the HO2 production from c-C5H9 + O-2 is similar to that previously observed in studies of C2H5 + O-2 and C3H7 + O-2 reactions. The-rate of formation for delayed HO2 production from c-G(5)H(9) + O-2 is larger than the rate of formation from either C2H5 + O-2, or C3H7 + O-2, at each temperature. However, apparent activation energies, obtained by an Arrhenius plot of the rates of formation for delayed HO2 formation, are very similar for the three systems (C2K5 + O-2, C3H7 + O-2, and c-C5H9 + O-2) The results suggest a similar coupled mechanism for HO2 production in the C2H5 + O-2, C3H7 + O-2, and c-C5H9 + O-2 reactions, with concerted elimination of HO2 from the RO2 radical responsible for HO2 alkene production.