This paper uses a new approach of retro-analysis. Typically policy is informed by forward-looking analysis of potential for alternative energy technologies. But historical knowledge of energy and processing requirements and greenhouse effects is more reliable for engineering evaluation of biofuel production systems. This study calculates energy inputs and greenhouse gas emissions for the most efficient biomass feedstocks in New Zealand if the policy had been implemented to maximize liquid biofuel production in the year 2004/2005. The study uses existing processing technologies and agricultural statistics. Bioethanol production is calculated from putrescible wastes and starch crops, and biodiesel production from rapeseed, tallow, wood and waste paper. Each production system is further evaluated using measures of land use, energy input, crop production related to the energy product, plus relative measures of efficiency and renewability. The research findings are that maximum biofuel production in 2004/2005 would have provided only a few per cent of demand, and would not have reduced dependence on foreign imported oil or exposure to fuel price rise. Finally, we conclude that demand management and efficiency are more effective means of meeting policy objectives. (C) 2013 Elsevier Ltd. All rights reserved.