Hydrogen has the potential to become the energy currency of the future. Biotechnological methods are being explored that can capture solar energy and store it as hydrogen. The hydrogenase enzyme, which combines protons and electrons to form hydrogen, is the key to these systems. Photosynthetic electrons can potentially be shuttled to hydrogenase via very direct engineered pathways. Unfortunately, photosynthetic oxygen production and hydrogen production must currently be separated temporally or spatially due to the deactivation of hydrogenase enzymes by oxygen. The highly active [FeFe] hydrogenases are particularly sensitive. We are using directed evolution to find oxygen-tolerant [FeFe] hydrogenase mutants that would relieve this limitation. We have recently developed an extremely high-throughput screening method based on our ability to activate the complex hydrogenase enzyme in a cell-free protein synthesis system. Our method is a modification of In Vitro Compartmentalization, in which emulsification of a reaction mixture into an oil phase results in isolation of individual genes in femtoliter-volume protein synthesis reactions. Subsequent emulsification of the water-in-oil emulsions into an aqueous phase gives water-in-oil-in-water double emulsions that can be sorted by FACS to screen millions of droplets per hour. We will discuss our work and present any oxygen-tolerant mutants that we identify between now and November.