Time-resolved production of HO2 and DO2 from the reactions of nondeuterated and deuterated ethyl and propyl radicals with O-2 are measured as a function of temperature and pressure in the "transition region" between 623 and 748 K using the technique of laser photolysis/long path frequency modulation spectroscopy. Experimental measurements, using both pulsed-photolytic Cl-atom-initiated oxidation of ethane and propane and direct photolysis of ethyl, n-propyl, and isopropyl iodides, are compared to kinetic models based on the results of time-dependent master equation calculations with ab initio characterization of stationary points. The formation of DO2 and HO2 from the subsequent reaction of the alkyl radicals with O-2 is followed by infrared frequency modulation spectroscopy. The concentration of I atoms is simultaneously monitored by direct absorption of a second laser probe on the spin-orbit transition. The kinetic models accurately describe the time scale and amplitude of the DO2 and HO2 formation resulting from C2D5 + O-2, n-C3D7 + O-2, i-C3D7 + O-2, and i-C3H7 + O-2. Overall, a very good level of agreement is found between theory and experiments over a wide range of temperatures, pressures, and O-2 concentrations. Good agreement is also found between previous literature studies and the theory presented in this work except in the case of the high-temperature rate coefficients for the reaction of i-C3H7 + O-2 to form propene. A reinvestigation of the high-temperature kinetics of the i-C3H7 + O-2 reaction appears warranted. The results from the present work suggest that the theory for formation of HO2 from the reactions of ethyl and both isomeric forms of propyl radicals with O-2 are very well established at this time. It is hoped that these reactions can now form the groundwork for the study and interpretation of larger and more complex R + O-2 systems.