Figure 2. Classification of transport biofuels.

First (1G) and second generation (2G) biofuels describe the origin of the biomass used to manufacture the fuel. 1G biofuels are produced from carbohydrate- or oil-rich food crops whereas 2G biofuels exploit a wider variety of non-comestible and lignocellulosic energy crops, waste lignocellulosic biomass (agricultural, forestry or sawmill residues) inedible or waste plant oils, spent cooking oil or rendered animal fats. Advanced biofuels, sometimes referred to as third- or fourth- generation (3G or 4G) biofuels, encompass a range of alternative biomass sources or combustible molecules derived from microbes, notably microalgae or oleaginous yeasts, or from metabolically engineered microbial cell factories. Figure drawn using Biorender software.