Biofuels come in different forms. Most common today are those derived from corn or from corn waste, however these are not the most ideal biofuels from a carbon cycle perspective. In Corn production, a huge amount of energy (derived from fossil fuels) is used to create corn yields. Thus, from a full carbon accounting perspective, it would be difficult to argue that corn production is carbon neutral at this time.
By contrast, Algae based biofuels offer the promise of creating a closed loop in the carbon cycle. That is, algae can take CO2 from the atmosphere and through photosynthesis create fatty lipids that can easily be transformed into useable fuels in existing or slightly modified combustion engines.
"Lipid production in Nannochloropsis gaditana is doubled by decreasing expression of a single transcriptional regulator", Nature Biotechnology (2017) doi:10.1038/nbt.3865, Published online 19 June 2017