Some hybrids get significantly better mileage than ordinary vehicles, but still run on conventional fuel.
As conventional fuel prices continue to rise, M&S expects these cost benefits to grow.
She estimates that they saved about $25,000 using the kitchen grease instead of conventional fuel.
She starts with a very thin membrane of the polymer used in conventional fuel cells.
A mixture of equal parts biofuel and conventional fuel will run one of the plane's engines.
Piquet, starting one position behind (16th), would be carrying a conventional fuel load, and stopping on laps 28 and 44.
Aviation biofuels still face hurdles, with criticism focusing on their environmental impact and their higher price than conventional fuel.
The White House noted that solar and wind energy prices are now becoming competitive with energy from conventional fuel sources.
China is building a repository for high-level nuclear waste, like conventional fuel rods, in the country's arid west.
To avoid misfuelling, diesel car owners could get a device that replaces the conventional fuel cap and prevents the petrol nozzle fitting in the tank.
In that scenario, he said, "it will not be possible to continue the supply monopoly, so the conventional fuel market will disappear, step by step".
