Xanthan gum fermentation is probably the most complex fermentation process in terms of theological property variations and associated mixing, power consumption, mass and heat transfer problems. In order to obtain these data, fermentations of Xanthomonas campestris were carried out on pilot scale bioreactor with different D/T ratios and different feeding strategies (batch and fed-batch). It was discovered that the theology of xanthan fermentation broth is of paramount importance to the above characteristics. The aerated power consumption and power number are both a function of aeration rate during the initial stage of the fermentation when the viscosity is low and the Reynolds number high. However when the broth becames viscous and Reynolds number less than or equal to 10(3), the gas velocity does not show any effect on the power number. The oxygen mass transfer coefficients and the overall heat transfer coefficients are both dependent on the impeller speed, the apparent viscosity of the broth and the D/T ratio. These data taken from practical fermentation will be useful for the design and scale up of fermenter for economic production of xanthan gum.