Jet stirred reactors (JSRs) are frequently employed for studying homogeneous gas phase chemical kinetics of fuels. The most challenging aspect of JSR is the achievement of sufficiently rapid mixing by turbulent jets so that the temperature and concentration fields inside the reactor could be considered homogeneous. However, there has not been any investigation in the literature which conclusively addresses that rapid mixing is indeed achieved. In this work, computational fluid dynamics (CFD) simulations for JSRs are conducted to gain insights into the dynamics of jet mixing. CFD simulations are conducted for some of the geometries commonly used by researchers and mixing inside the reactor is visualized by computationally tracking an inert tracer pulse. Results suggest that some of the commonly used reactors could have significant concentration non-homogeneity and therefore may not be suitable for chemical kinetic studies. For conditions when the flow in the reactor is sufficiently turbulent and recycling rate is high, back mixing can become problematic even though the concentration field is more or less homogeneous. As a consequence, the vast chemical kinetic data obtained from such facilities is questionable. Furthermore, modifications to the design of JSR are considered that could significantly improve concentration homogeneity. An alternative geometry of the reactor is evaluated and shown to be promising. A new JSR is designed and fabricated for studying homogeneous gas phase chemical kinetics over a range of pressures from atmospheric to elevated (up to 50 bar).