The biomass production and biochemical properties of marine and freshwater species of green macroalgae (multicellular algae), cultivated in outdoor conditions, was evaluated to assess the potential conversion to high-energy liquid biofuels, specifically biocrude and biodiesel, and the value of these products. Biomass productivities were typically 2-times higher for marine macroalgae (8.5 - 11.9 g m−2 d−1, dry weight) than for freshwater macroalgae (3.4 - 5.1 g m−2 d−1, dry weight). The biochemical compositions of the species were also distinct, with higher ash content (25.5 - 36.6%) in marine macroalgae and higher calorific value (15.8 - 16.4 MJ kg−1) in freshwater macroalgae. Lipid content was highest for freshwater Oedogonium and marine Derbesia. Lipids are a critical organic component for biocrude production by hydrothermal liquefaction (HTL) and the theoretical biocrude yield was therefore highest for Oedogonium (17.7%, dry weight) and Derbesia (16.2%, dry weight). Theoretical biocrude yields were also higher than biodiesel yields for all species due to the conversion of the whole organic component of biomass, including the predominant carbohydrate fraction. However, all marine species had higher biomass productivities and therefore had higher projected biocrude productivities than freshwater species, up to 7.1 t of biocrude ha−1 yr−1 for Derbesia. The projected value of the six macroalgae was increased by 45 - 77% (up to US$7,700 ha−1 yr−1) through the extraction of protein prior to the conversion of the residual biomass to biocrude. The present study highlights the importance of optimising biomass productivities for high-energy fuels and targeting additional co-products to increase value. This article is protected by copyright. All rights reserved.