This study estimates the carbon source costs for producing xanthan and lactic acid on alternative potato residues media and assesses the potential for profitability and social net benefits of xanthan and lactic acid fermentations. Xanthan fermentations were conducted in solid and semi-solid mode where there was 60-240 kg dry matter t (1) of potato residues. Average xanthan yield was 249 g kg(-1) dry matter, with standard deviation of 149 g kg(-1). Lactic acid fermentations were conducted in submerged mode with starch concentrations of 30-60 kg m (3). Nine to 54 kg of the starch was fermented to lactic acid with average conversion efficiency of about 60 percent. Fermentation of the residues into xanthan or lactic acid could generate profit and net social benefits; the potential for positive externalities emanates from: i) reducing environmental costs of the residues disposal, and ii) alleviating the pressure on materials that are both conventional media for xanthan and lactic acid fermentations and inputs in subsidized markets for food and fuel. Published by Elsevier Ltd.