Phosphorus-containing compounds (PCCs) have been found to be significantly more effective than CF3Br for reducing burning velocity when added to stoichiometric hydrocarbon-air flames. However, when added to lean flames, DMMP (dimethylmethylphosphonate) is predicted to increase the burning velocity. The addition of DMMP to lean mixtures apparently increases the equivalence ratio (fuel/oxidizer) and the combustion temperature, as a result of hydrocarbon content of DMMP molecule. Premixed flames studies with added DMMP, OP(OH)(3), and CF3Br are used to understand the different behavior with varying equivalence ratio and agent loading. Decrease of the equivalence ratio leads to the decrease of inhibition effectiveness of PCCs relative to bromine-containing compounds. For very lean mixtures CF3Br becomes more effective inhibitor than PCCs. Calculations of laminar burning velocities for pure DMMP/air mixtures predict the maximum burning velocity of 10.5 cm/s at 4.04% of DMMP in air and at an initial temperature of 400 K. Adiabatic combustion temperature is 2155 K at these conditions. (C) 2016 The Combustion Institute. Published by Elsevier Inc. All rights reserved.