A fuel management system of a vehicle and a refueling system for gasoline stations to handle a fuel system for improved fuel efficiency which can be contained in a fuel tank having a gasoline phase comprises gasoline or gasohol; and an anti-knock phase comprising an anti-knock agent comprising a glycol anti-knock subagent, water and one or more of a second anti-knock subagent selected from the group of methanol, ethanol and mixtures thereof; such that the anti-knock agent phase is substantially immiscible with the gasoline phase.