Over the last decade, the production and consumption of biofuels increased rapidly worldwide, in an attempt to reduce GHG (greenhouse gas) emissions, diversify transportation fuels, promote renewable energy, and create or maintain employment, especially in rural areas and developing countries. Although policy instruments being currently implemented in industrialized regions focus on sustainable biofuels, the definition and assessment of sustainability remains a highly debated issue. Several countries have adopted compulsory targets or financial incentives for promoting biofuels, and only a few countries have accounted for sustainability certification schemes for those biofuels within their policy framework. In this paper, a logic-based model for assessing the sustainability of biofuels is presented. The model uses a hierarchical structure to link multiple factors from the more specific variables to the most general one, sustainability performance. The strengths and limitations of the model are discussed and the anticipated improvements are provided. (C) 2010 Elsevier Ltd. All rights reserved.