This study evaluated the composition, digestibility [dry matter digestibility (DMD)], CH₄ abatement potential, and fatty acid biohydrogenation of six species of microalgae. Lipid content ranged from 115 g kg^-1 dry matter (DM) (Scenedesmus sp. AMDD) to 361 g kg^-1 DM (Tetracystis sp.), while Scenedesmus sp. AMDD had the highest carbohydrate (364 g kg^-1 DM) and fibre content (277 g kg^-1 DM). Gas production was highest (P < 0.001) for Micractinium reisseri and Chlorella vulgaris. In vitro DMD ranged from 654 g kg^-1 for Scenedesmus sp. AMDD to 797 g kg^-1 for Nannochloris bacillaris. Total CH₄ differed (P < 0.001) among microalgae, ranging from 1.76 mL g^-1 DM for Tetracystis sp. to 4.07 mL g^-1 DM for M. reisseri. Nannochloropsis granulata (marine) had higher myristic, palmitoleic, and eicosapentaenoic acid levels than freshwater microalgae. Levels of a-linolenic acid were higher in Scenedesmus sp. AMDD than all other microalgae. CH₄ production negatively correlated (P < 0.05) with levels of total carbohydrate, oleic, and a-linolenic acid. Despite having a lower lipid content, CH₄ reductions with Scenedesmus sp. AMDD were comparable to Tetracystis sp. and N. bacillaris. Reductions in CH₄ with Tetracystis sp. and N. bacillaris occurred without a decline in DMD, suggesting that overall microbial activity was not inhibited.