the carnot efficiency dictates that higher efficiencies can be attained by increasing the temperature of the steam. sub-critical fossil fuel power stations can achieve 36–40% efficiency. supercritical designs have efficiencies in the low to mid 40% range, with new "ultra critical" designs using pressures of 4400 psi (30.3 mpa) and multiple stage reheat reaching 45-48% efficiency. above the critical point for water of and 3212 psi (22.06 mpa), there is no phase transition from water to steam, but only a gradual decrease in density.