Kinetic and product branching data have been measured for the reaction of CH3O2 radicals with C10 in the temperature range 225-355 K using the discharge-flow/mass spectrometry technique. The pressure-independent overall reaction rate constant is described by k (12)(225-355 K)=(3.25 f 0.50) X 10-12 exp ((-114 & 38)/T) cm3 molecule-'sl. Two reaction channels were identified, leading to CH30+ ClOO (12a) and CHJOCl+ 0 2 (12b), ...