A numerical and experimental study was conducted, with the purpose of inferring the influence of the CO2 concentration (xCO(2)) for different equivalence ratios (phi) on CH4/CO2/air (biogas) flames chemiluminescence. A thorough analysis on the signals of OH*, CH*, C-2(*) and CO2 was performed. Typical biogas compositions were tested under laminar atmospheric flame conditions, within the unburned equivalence ratio of 0.9 and 1.14 with CO2 concentrations up to 40% in the blend. Experimental measurements of chemiluminescence were done using spectroscopy in the UV-visible region of the spectra. Simulations were performed with the GRI-Mech 3.0 mechanism without accounting for the nitrogen chemistry, extended with a chemiluminescence kinetics of OH*, CH*, C-2(*) and CO2*, in a burner-stabilized frame in CANTERA. Experimental measurements and numerical simulations are compared and generally are in good agreement. It was verified that CO2 dilution leads to a regular decrease in the emission intensities of OH*, CH*, C-2(*) and CO2*. Relations between chemiluminescence intensity ratios and xCO(2) and. were found. It was shown that OH*/CO2* and C-2(*)/CO2* have the potential predict xCO2 in CH4/CO2/air flames. Moreover, it was verified that OH*/CH*,OH*/C-2(*) and CH*/C-2(*) are well suited to infer. for the blends tested. It was verified that xCO(2) does not cause relevant changes in the chemiluminescence ratios when inferring..