How are biofuels to be certified as produced in a sustainable and responsible fashion? In the global debate over this issue, one party to the proceedings seems rarely to be mentioned-namely the commodities exchanges through which a global biofuels market is being created. In this contribution, I propose a Solution to the problem of sustainability certification through a biofuels futures contract equipped with 'proof of origin' documentation. The proposal does not call for any radical break with current practice, extending existing certification procedures with a requirement for the vendor to provide documentation, probably in barcoded form, of the history of the biofuel offered for sale, including plantation and biorefinery where the biofuel was produced and subsequent blendings it may have undergone. The proposal is thus compatible with the blending practices of large global traders, whose activities are the source of the difficulties of other approaches to certification. It is argued that if such a sustainable futures contract for bioehanol (in the first instance) were to be introduced, then it would likely trade at a premium and become the primary vehicle for North-South trade in biofuels. (C) 2008 Elsevier Ltd. All rights reserved.