Manufacturing engineering is supposed to provide analyses related to various aspects of manufacturing and production in order to maximise technological, energy, and economic gains in relevant production processes. The present paper gives a recapitulation of several publications by present authors, presenting considerations of the energy efficiency of biofuel production. The energy efficiency is understood as the ratio of energy obtained from biofuels produced basing on crops from a particular area to the energy required to satisfy needs of all subsidiary processes assuring correct functioning of the production system, starting from operations aimed to obtain agricultural crops, and ending with the conversion of the crops onto biofuels. Derived by the present authors, the mathematical model of energy efficiency of biofuel production is extended to a more general form, and applied to the analysis of quantitative relations between energy efficiency of sc. "energy plantations", and further elements of biofuel production system converting harvested biomass into biofuel. Investigations are aimed towards the determination of the role of biomass as a source of energy.