A fuel reservoir having a reticulated material, generally a felt or a foam, disposed therein is provided. The addition of this reticulated material, either alone or in combination with a viscous fuel, assists the prevention of undesired flow of the fuel, the minimization of undesired leakages, and assists in orientation independence and uniform distribution of the fuel in the reservoir. The reticulated material enables the use of a viscous liquid fuel that has fuel diffusion rates and fuel utilization characteristics that approach those of neat liquid methanol. The material also helps create a greater surface area for evaporation, thus allowing a highly concentrated, vaporous fuel substance to be delivered to an associated fuel cell.