The entrainment into a turbulent jet in coflow is directly measured using Particle Image Velocimetry (PIV). The direct measurement technique is verified by comparing with the measurement with previous results for free jets. By measuring the velocity from the outside of the main jet, the entrainment measurement does not suffer from density fluctuations in reacting jets. The effects of coflow speed, heat release and buoyancy on the entrainment rate are investigated. The increase in coflow speed reduces the entrainment for both reacting and non-reacting jets. Heat release suppresses entrainment by a factor of 2.6 when compared to the non-reacting jet, but buoyancy recovers the entrainment to a faster rate. Therefore, for the initial part of a reacting jet where the jet is momentum driven, heat release has dominant effect on entrainment, but buoyancy compensates the reduction further down-stream of the jet.