Concerns over climate change have led to the promotion of biofuels for transport, particularly biodiesel from oilseed crops and ethanol from sugar and starch crops. However, the climate-change mitigation potential of the various biofuels estimated in published studies tends to vary significantly, questioning the reliability of the methods used to quantify potential impacts. We investigated the values published in the European Commission’s Renewable Energy Directive (RED), and recalculated the climate-change impacts of a range of biofuels using internally-consistent attributional and consequential modelling approaches to enable comparison of these approaches. We conclude that the estimated results are highly dependent on the modelling approach adopted, to the detriment of the perception of the robustness of life cycle assessment as a tool for estimating the climate-change impacts of biofuels. Land use change emissions are a determining parameter which should not be omitted, even if modelling it introduces a large variability in the results and makes interpretation complex. Clearer guidelines and standardization efforts would be helpful in the harmonization of LCA practice, so that the results can be more useful, robust and reproducible.