The NO3 product yield in the reaction O(P-3) + BrONO2 was measured to be >0.85 at 298 K. Yield measurements were made using the technique of laser-pulsed photolysis with long-path transient absorption detection of NO3. O(P-3) atoms were produced in the presence of BrONO2 by the 248-nm photolysis of O-3 in a N-2 bath gas. The photolysis laser fluence was calibrated using N2O5 as an actinometer.