Biomethane is an energy vector suitable for renewable transport fuel which may derive energy through three different methodologies: thermal gasification; biological anaerobic digestion; and conversion of electricity to hydrogen (via electrolysis) and on to methane as described by the Sabatier Equation. Thermal gasification to produce methane (based on "hard" feed stock) tends to require significant scale, of the order of 400 MW. Biological anaerobic digestion (based on "soft" feed stock) is typically of scale less than 1 MW. Systems based on the Sabatier Equation convert hydrogen to methane exothermically and sequester carbon. The resource is assessed at 19% of energy in transport in Ireland. Adopting the approach of the EU Renewable Energy Directive (for example double credit for biofuels from residues and lignocellulosic feed stock) biomethane can supply 40% renewable energy supply in transport (RES-T). The resource is sufficient to supply 30% of the private transport fleet with indigenous sustainable gaseous biofuel. (C) 2013 Elsevier Ltd. All rights reserved.