Net energy (NE) output, external cost to society of emissions, total production costs, and the renewability of a fuel are four critical factors that should be taken into account while developing sustainable energy resource systems. For this purpose, a new indicator, CNERλ,(Cost of Net Energy taking into account the Renewability) is proposed in this paper. The mixture of 85% ethanol (derived from corn) and 15% gasoline by volume (E85) and conventional gasoline (CG) are selected as assessing cases for illustrating the application of the new indicator. The CNERλ of E85 is 0.885, i.e. 12.5% lower than that of CG. It is shown that E85 is a more sustainable option comparing with CG by using the novel assessment indicator.