Energy Input–Output Meta-Analysis Reveals Algal Diesel Struggles to Break Even

Algal biofuels have been investigated as an alternative to fossil fuels and first-generation biofuels for transportation in the United States since the 1970s. Yet after five decades of development, scalability and implementation remain limited—largely due to persistent barriers such as low biomass productivity, modest lipid yields, and energy-intensive processing methods. These technical challenges significantly constrain the feasibility of large-scale commercialization despite substantial research and investment. To evaluate progress toward commercial viability, this study harmonized energy inputs and outputs across 508 observations on the production of algal biofuel energy return on energy investment (EROEI) in the United States. While bioethanol achieves an EROEI of (2.8) and oil (8.7), the analysis produced a mean EROEI of 1.01—essentially the break-even point—irrespective of system boundaries. Life-cycle analysis results showed that hydrothermal liquefaction in algal diesel production yielded a slightly higher mean EROEI (0.67) than transesterification (0.51), yet both showed net energy losses. Co-products were found to increase EROEI values, particularly when recycled into production processes. Collectively, these findings indicate that research and development to date has not produced a technology with net energy gains sufficient for commercial viability. For this reason, algal biofuels show little potential to alleviate the ongoing decline in the EROEI of petroleum and are not a promising renewable energy option for reducing greenhouse gas emissions from the transportation sector. They also show little promise for alleviating the land use, food vs. fuel and other controversies that have plagued first and second-generation biofuels.