Pyrolysis oil, commonly known as bio-crude or bio-oil, is a synthetic fuel being researched as a petroleum substitute. Although not as stable as fossil fuel, bio-oil produced from microalgal waste biomass is more stable than that produced from traditional crops (e.g., wood). Another important biofuel is bio-oil, which is produced through thermochemical conversion of biomass, such as pyrolysis and hydrothermal liquefaction. Because of its high energy density and ease of storage and transportation compared to gaseous products, bio-oil has been considered a possible feedstock to replace petroleum fuel for power generation. Bio-oil can also be utilized as a direct fuel in diesel or gas turbine engines. Furthermore, as compared to petroleum-based fuel, bio-oil is biodegradable, CO2 or greenhouse gas neutral, and produces substantially less NOx and SOx when combusted in an engine. As a result, bio-oil is a green fuel with environmental benefits.