We investigated the limits and extent of lubricants biodegradation at different nutrient conditions and evaluated several soil biological activities with regard to their usefulness for monitoring the bioremediation process in a soil contaminated with lubricants. To examine the effects of nutrient addition on lubricants biodegradation, a bench-scale investigation was conducted under different nutrient conditions for over 105 days testing period. When nutrients were added to contaminated soil with aged lubricant, great stimulation was occurred in fertilized soil for hydrocarbon degradation activity compared to non-fertilized soil. At the end of the experiment (105 days after), the initial level of contamination (9320 +/- 343 mg/kg) was reduced by 42-51% in the fertilized soil, whereas, only 18% of the hydrocarbon was eliminated in the non-fertilized soil. The effect of biostimulation of indigenous soil microorganisms declined with time, apparently 42% of the initial concentration of hydrocarbon remained at the end of experiment. Lubricants biodegradation process could be monitored well by soil biological parameters. In fertilized soil, biological parameters (number of HUB, soil respiration, dehydrogenase and catalase activities) were significantly enhanced and correlated with each other, as well as the residual lubricant concentration. (C) 2006 Elsevier B.V. All rights reserved.