R Holmes, Less than zero, NewScientist, 8 December 2012, p 34]

In the biofuels world, it is noteworthy that current experimental methods achieve their results within a single day of operation compared with the 400 million years taken by geology. Furthermore, if both a carbon-containing fuel and some carbon sequestration result, the overall outcome is carbon negativity. In Spain, Bio Fuel Systems uses blue-green algae (cyanobacteria) together with CO2 from a cement factory flue to make Blue Petroleum, producing daily 2.5 barrels of crude oil per hectare. In US, Algae Systems culture algae in plastic bags floating near the sea shore, whereas Cool Planet Energy Systems have developed a system of pyrolysis to convert biomass directly into the hydrocarbon types found in conventional petroleum fuels. Excess CO2 can be sequestered either by burying or by conversion to biochar and returned to the soil where it enhances crop yields by retaining water and nutrients.