The most fuel efficient hybrid for sale in the US gets 51 MPG, but a startup called Transonic Combustion claims they can improve that. They claim their fuel-injection system will get 64 MPG.
Transonic's fuel-injection system is supposedly better because it "uses supercritical fluids and requires no spark to ignite the fuel. The supercritical fluid is mixed with air before injected into the cylinder. The heat and pressure, in the cylinder, alone is enough to cause the fuel to combust without a spark." That spark-free ignition process along with some proprietary software makes this particular fuel-injection system different from direct injection systems and supposedly helps make it so ultra-efficient.
Transonic says that they hope to place the technology in production cars by 2014, but I really just want to see the data from their initial test, because this is an almost bold claim for mainstream electric hybrids. [PhysOrg]