Methods of optical emission spectroscopy (OES) are used to determine basic parameters of the plasma jet such as temperature, electron number density, and mole fractions of plasma components. The analysis is based on the measurement of a large variety of argon, oxygen and hydrogen spectral lines in the whole visible spectral region for various operating conditions. The electron number density is determined from a profile of Hp line. The temperature is obtained from Boltzmann diagrams and from the ratio of atomic and ionic lines. A discrepancy is found in evaluation of the excitation temperature from certain argon ionic lines. The mole fraction of oxygen significantly decreases towards the jet centerline. This effect increases with increasing temperature gradient, and is explained mainly as a result of inhomogeneous mixing of argon and water in the stabilizing channel of the torch.