A simple first order kinetic model has been developed for steam distillation of lemongrass (Cymbopogon spp.). This rate model was tested on pilot scale, steam distillation units, with lemon grass batches of 70 to 1000 kg. For intimate contact of lemongrass and steam, two improved direct steam spargers were provided in these units. It is observed, that, the loose packing of plant material inside distillation still and steam injection rate, increases the oil yield. Straight line behaviour with intercept on time axis of the above rate model explains, that, oil production inside the distillation unit is not instantaneous, but some time is required for wetting of grass for the diffusion and osmosis of oil.