Graphene is studied as an oxidation barrier coating for liquid and liquid-vapor phase-change cooling systems. Forced convection heat transfer experiments on bare and graphene-coated copper surfaces reveal identical liquid-phase and two-phase thermal performance for the two surfaces. Surface analysis after thermal testing indicates significant oxide formation on the entire surface of the bare copper substrate; however, oxidation is observed only along the grain boundaries of the graphene-coated substrate. Results show that few-layer graphene can act as a protective layer even under vigorous flow boiling conditions, indicating a broad application space of few-layer graphene as an ultra-thin oxidation barrier coating. (C) 2012 Elsevier Ltd. All rights reserved.