Chemical inhibition of laminar propane flames by organophosphorus compounds has been studied experimentally, using a laboratory Mache Hebra nozzle burner and a flat flame burner with molecular beam mass spectrometry (MBMS), and with a computational flame model using a detailed chemical kinetic reaction mechanism. Both fuel-lean and fuel-rich propane flames were studied to examine the role of equivalence ratio in flame inhibition. The experiments examined a wide variety of organophosphorus compounds. We report on the experimental species flame profiles for tri-methyl phosphate (TMP) and compare them with the species flame profile results from modeling of TMP and di-methyl methyl phosphonate (DMMP). Both the experiments and kinetic modeling support and illustrate previous experimental studies in both premixed and non-premixed flames that inhibition efficiency is effectively the same for all of the organophosphorus compounds examined, independent of the molecular structure of the initial inhibitor molecule. The chemical inhibition is due to reactions involving the small P-bearing species HOPO{sub 2} and HOPO that are produced by the organophosphorus compounds (OPCs). The ratios of the HOPO{sub 2} and HOPO concentrations differ between the lean and rich flames, with HOPO{sub 2} dominant in lean flames while HOPO dominates in rich flames. The resulting HOPO{sub 2} and HOPO species profiles do not depend significantly on the initial source of the HOPO{sub 2} and HOPO and thus are relatively insensitive to the initial OPC inhibitor. A more generalized form of the original Twarowski mechanism for hydrocarbon radical recombination is developed to account for the results observed, and new theoretical values have been determined for heats of formation of the important P-containing species, using the BAC-G2 method.