For so long our choices in automobiles have been limited to what style, make and color, but looking out on the horizon the question: “What kind of car do you want?” will take on a whole other meaning.

Of course there was always a gasoline/diesel option and a high grade versus low-grade fuel decision to make at the pump — but as automotive manufacturers are expanding their lines into the alternative fuel and engine arena our options are about to get more diverse and perhaps a bit confusing. Although most experts and many automotive manufacturers portend that hydrogen will be the industry standard, the transition period from petroleum-only fuel is offering many choices.

Today, there are hybrids, plug-in hybrids, flex-fuel, bio-diesel, straight vegetable oil, electric, hybrid electric, natural gas and propane, and, at least in proto-type, hydrogen fuel cell and hydrogen combustible engines.

Whether the future brings us one industry standard engine-type and/or fuel source or creates an array of engines and fuel types, it’s worth it to be familiar with the options. The following is a quick primer to alternatives to petroleum-only vehicles:

Petroleum electric hybrid vehicle
A petroleum electric hybrid vehicle uses a rechargeable energy storage system and a fuel for propulsion. Full hybrids use the combustion engine to spin an electrical generator in order to recharge a battery or directly feed power to an electric motor and shuts down the engine when idling.

Plug-in hybrid
Plug-in hybrid electric vehicles have energy that can be recharged by connecting to an electrical power source. Plug-in hybrids have both conventional hybrid electric vehicles and battery electric vehicles. As of April 2007, plug-in hybrid passenger vehicles are not in mass production. However, Toyota and General Motors have both announced plans to introduce production as early as 2009.

Flex-fuel vehicle
Some flexible-fuel vehicles alternates between two sources of fuel, with separate tanks for each. The most common flex-fuel vehicles can accept gasoline mixed with varying levels of ethanol (E85). Some vehicles carry a natural gas tank and can switch from gasoline to gas. The fuel mixture type is automatically detected by sensors that tunes the timing of spark plugs and fuel injectors. Over 4 million flexible-fuel vehicles are currently operating.

Electric car
Electric vehicles uses energy stored in rechargeable battery packs with an electric motor alone or in conjunction with an internal combustion engines to power the vehicle. Electric cars can charge from the power grid. Times between charging depend on battery type and can range from 20 to 50 miles. Some are capable of up to 80 miles per charge. New lithium-ion batteries are said to achieve 250 to 300 miles per charge.

Biodiesel
Biodiesel refers to non-petroleum fuel that can be used in diesel engines. Biodiesel refers to alkyl esters made from the transesterification of vegetable oils or animal fats, it is biodegradable and non-toxic, and produces about 60 percent less net carbon dioxide emissions than petroleum diesel.

Straight vegetable oil/waste vegetable oil
Many vegetable oils have similar fuel properties to diesel fuel. Vegetable oil discarded from a restaurant and used as fuel is called waste vegetable oil. It is different from biodiesel because diesel engines that use straight vegetable oil need specific engine modifications.

Hydrogen fuel cell vehicles
Hydrogen fuel cell vehicles use fuel cells and electric motors instead of the traditional combustible engine. Hydrogen used as fuel reacts with oxygen inside the fuel cells and produces electricity to power the engine. Hydrogen is produced utilizing natural gas, coal, liquefied petroleum gas, biomass or from water by electrolysis.

Internal combustion hydrogen vehicles
Hydrogen internal combustion engines are a slightly modified version of the traditional gasoline internal combustion engine. Hydrogen engines burn fuel in the same manner as gasoline engines. Hydrogen can also be used in as a mixture in fuel, and can increase efficiency and reduce emissions. This process requires a number of modifications to existing engine air/fuel and timing controls.