Sulfur-based autotrophic denitrification and denitritation were investigated using an oil reservoir culture. In batch system nitrate up to 20 mM was reduced with concomitant sulfate production. With 20 mM nitrate, reduction of produced nitrite did not occur which was contrary to that under heterotrophic conditions. Reduction of nitrite as the sole substrate occurred even at 50 mM. When both sulfur and acetate were present, only acetate was used as the electron donor. In the continuous biofilm reactor maximum nitrate and nitrite removal rates of 17.3 and 13.2 mM/h, much higher than literature values, were achieved at residence times of 0.4 and 0.6 h, respectively. Bicarbonate functioned effectively as carbon source and alkaline, and eliminated the problems associated with lime addition. Based on these and our earlier findings the highest nitrate and nitrite removal rates are achieved under heterotrophic conditions with acetate, followed by autotrophic rates with sulfide, and then elemental sulfur. (C) 2012 Elsevier Ltd. All rights reserved.