While biofuels themselves consist solely of energy photosynthesized with sunlight, producing them requires human effort and outside energy resources. Farmers capture the ‘free’ energy of the sun by seeding, watering and fertilizing plants. The biomass that grows must then be harvested, transported and refined into a liquid fuel. All of these activities use energy; but people can choose between more and less efficient biofuel production pathways. Some feedstocks are more efficient and easier to process than others, and some farming and refining methods are more energetically frugal than others.