US patent number 7490593 is a patent that seems to fail the "utility" criteria for patentability in the USA. Note: this is not a software patent.
 Magnetic conditioning apparatus for diesel engine fuel
A magnetic conditioning device for diesel engine fuel includes a housing element, placed along the fuel feeding line, having a fuel inlet and a fuel outlet, and providing a septum in correspondence of the inlet to deviate the inlet fuel, and an obliged path for the fuel, being provided at least two opposed magnetic elements. Along the obliged path, a magnetic field is induced on the flowing fuel.
The US Patent Office requires that the device be "useful". This device cannot work as described, as magnets of the type described have no effect on hydrocarbons. Tests have been carried out by several organizations:
- CNN - No shortcuts to saving money on gas
- Mythbusters - Episode 53 Part 2 - The Great Gas Conspiracy
- Popular Mechanics - Looking For A Miracle: We Test Automotive 'Fuel Savers'
 Final Note
While magnets can affect hydrogen in theory (see Bussard Ramjet), the size of magnet needed to produce a field that strong would make it impractical to build on a planetary surface. This does not however stop dreamers, most of whom know no science, from trying magnets. There's something about magnets that just draws peoples attention, and this is illustrated by there being several thousand "Fuel Magnet" patents in the USPTO database.