Hydrogen production was measured from viable wild-type and M55 mutant cells of Synechocystis sp. PCC 6803 encapsulated in silica sol-gel derived from tetraethoxysilane, tetramethoxysilane, and a mixture of tetra ethoxysilane with methyltriethoxysilane. Glycerol and polyethylene glycol were used as additives in concentrations up to 14 wt.% to increase porosity and pore connectivity and to reduce stress on the encapsulated cells. Mixtures were evaluated for hydrogen production in a high-throughput screening assay, and samples were imaged with environmental scanning electron microscopy. Compositions showing improved H(2) production were selected for further study via quantitative analysis of H(2) production in GC vial assays. H(2) production activity was monitored for up to 5 days and H(2) production from encapsulated cells was observed at levels comparable to or exceeding cells suspended in liquid media. (C) 2008 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.