The critical oxygen concentration (COC) in this study is defined as the maximum oxygen concentration at which a mixture of methanol vapor in nitrogen does not explode, regardless of the nitrogen concentration in the mixture. This paper presents data on the critical oxygen concentration (COC), in the presence of added N-2, of methanol (CH4O) saturated vapor mixtures at elevated temperature and pressure. We have used a COC measurement system consisting of a 4-L explosion vessel, an ignition subsystem, and a transient pressure measurement subsystem. Through a series of experiments carried out in this system, the COCs of methanol-saturated vapor/O-2/N-2 mixtures at different initial pressures and an elevated temperature of 80 degrees C have been studied, and the influence of concentration of nitrogen on the COG has been analyzed and discussed. Variation of the initial pressure within the studied range was found to have significant effect on the COCs of the methanol saturated vapor/O-2/N-2 mixtures. There is a very large difference between the COCs (or CNCs) of the methanol-saturated vapor/O-2/N-2 mixtures at the elevated temperature and pressure and those of methanol vapor in air at atmospheric pressure and room temperature. The COCs of the methanol-saturated vapor/O-2/N-2 mixtures with the initial temperature of 80 degrees C at the initial pressure of 0.5, 0.4, and 0.3 MPa are 36, 28, and 21 vol %, respectively. The corresponding CNCs at initial pressures of 0.5, 0.4, and 0.3 MPa are 54, 59.5, and 62 vol %, respectively.