Experiments have been conducted to investigate the influence of a horizontal air jet on the performance of a fluidized bed coal combustor. Cold flow model studies were first made to visually and photographically study the effect of jet penetration on bed solids circulation patterns and mixing characteristics. Using these cold flow model studies as a basis, the influence of jet penetration and jet induced solids circulation on the combustion characteristics of a high sulfur coal has been investigated in an identical fluidized bed combustor. The experiments show that the combustion efficiency and bed temperature are usually higher at low jet air mass flow rates. The importance of the synergistic influence of bed solids blending rate, the elutriation rate, the superficial velocity, and the chemical reaction rate in realizing high combustion efficiencies is demonstrated. Pf PP Nomenclature= nozzle diameter, m = mean particle diameter, m = gravitational constant jet penetration depth from end of nozzle, m = jet air velocity, m/s = bed void fraction = gas density, kg/m 3 = bed solid particle density, kg/m 3