Abstract Vertical, round turbulent jets with combined effects of buoyancy and mutual hindering are investigated by an integral method. The method avoids application of an empirical entrainment coefficient by including the differential equations of motion and energy at the jet axis. Mutual hindering of jets in a spatially periodic arrangement is shown to give rise to significant deviations from single jet behaviour. In the absence of buoyancy forces, the flow would decay exponentially with increasing distance from the jet origin. In the case of buoyancy-enhanced jets, however, a transition to a cellular flow driven by natural convection is predicted.