Spatial distributions of plasma parameters are presented for a H-2/Ar plasma jet with addition of methane. The plasma has been generated at atmospheric pressure by a 200 A (20 kW) nontransferred dc arc. Optical emission spectroscopy has been used for the measurements assuming the plasma jet to be optically thin and to have an axial symmetry. Local spectral emissivity values have been evaluated using a routine Abel inversion procedure. Half-width and emissivity of H-beta spectral line have been measured to determine the electron density and temperature of the plasma. The densities of excited C-2, CH radicals have been evaluated from the absolute emissivities of relevant molecular emission bands measured in limited spectral intervals in the visible spectrum. The emissivity ratios have been used to find rotational and vibrational temperatures. The results supply information on methane decomposition and the behavior of molecular radicals in close-to-thermal plasma jets.