The thermal decomposition of the 5-methyl-2furanylmethyl radical (R,), the most important primary radical formed during the combustion and thermal decomposition of 2,5-dimethylfuran (a promising next-generation biofuel), was studied using CBS-QB3 calculations and master equation (ME)/RRKM modeling. Because very little information is available in the literature, the detailed potential energy surface (PES) was investigated thoroughly. Only the main pathways, having a kinetic influence on the decomposition of R-1, were retained in the final ME/RRKIvl model. Among all the channels studied, the ring-opening of the 5-methyl-2-furanylmethyl radical, followed by ring enlargement to form c-yclohexadienone molecules is predicted to be the easiest decomposition channel of R-1. The C-6 cyclic species formed can undergo unimolecular reactions to yield phenol and to a lesser extent cyclopentadiene and CO. Our calculations predict that these species are important products formed during the pyrolysis of 2,5-dimethylfuran (DMF). Other channels involved in the decomposition of R-1 lead directly to the formation of linear and cyclic unsaturated Cs species and constitute an additional source of cyclopentadiene and CO. High-pressure limit rate constants were computed as well as thermochemical properties for important species. ME/RRKM analysis was performed to probe the influence of pressure on the rate coefficients and pressure dependent rate coefficients were proposed for pressures and temperatures ranging, respectively, from 10(-2) bar to 10 bar and 1000 to 2000 K.