Aims: Xanthan production by Xanthomonas campestris from several olive mill wastewaters (OMW) was investigated. Methods and Results: Maximum xanthan production of 4 g 1(-1) was obtained in media with 50% OMW as sole source of nutrients. OMW storage decreased effluent quality for xanthan production. The range of effluent concentration for X. campestris growth and xanthan production varied depending on OMW extraction method. Wastewaters from press and two-phase extraction methods required higher dilution rates (< 10%) than those from the three-phase extraction method (50%). Nitrogen supplementation improved xanthan production in press and two-phase OMW. Conclusions: Factors affecting wastewaters composition, namely, waste storage, time of olive harvesting, and method for oil extraction, were found to influence xanthan production in shake-flask cultures. Significance and Impact of the Study: Conditions for xanthan production from OMW should be optimized in accordance with the nature of the waste material.