The jet flow fields reported on in this paper were created by an unconventional gun head intended for polymer powder flame deposition. These flow fields are discussed in earlier papers by Payne et al. This paper reports on how the air or CO2 used in place of propane with this gun head mixed inertly with an isothermal coaxial air jet. Flow visualization with a sheet of laser light described by Payne et al. showed that the jets, air or CO2, emanating from the propane nozzles were rapidly entrained in the coaxial air jet regardless of the presence or absence of a particle stream from the central nozzle. A gas analyzer measured the gas composition in the flow field downstream of the entrainment volume. The time-averaged CO2 concentration on the nominal centreline of the jet was constant or nearly so. In contrast, the variation in CO2 concentration increased dramatically with the radius at which the gas was sampled, up to a radius of similar to 1.5cm at a distance of 10cm from the nozzle, after which this fluctuation decreased to 0 at the edges of the flow field. The magnitude of these fluctuations also decreased with the axial distance changing from 10 to 30 cm. Again, the presence or absence of a particle stream from the central jet nozzle had very little effect on the amount of CO2 measured. The irregular entrainment of CO2 caused the variations in the CO2 measured in the flow field.