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The Clean Cities Coalition, which is dedicated to petroleum reduction, recognizes seven alternative fuels officially and defines them on their national website:

  1. Biodiesel
  2. Electricity
  3. Ethanol
  4. Hydrogen
  5. Methanol
  6. Natural Gas
  7. Propane

(Please note that clicking on the above links will open a new window where the above alternative fuels are defined and summarized on the National Clean Cities Coalition website.)


Alternative Fuel Comparison
Pro's and Con's at a Glance

by Wise Gas, Inc.
Alternative Fuel Definition: Pro's Con's
Biodiesel is a renewable fuel made from vegetable oil or animal fats, including soybeans, canola oil, and even used cooking oil.


  • Benefits the Environment
  • Slightly reduces diesel usage
  • Biodiesel is biodegradable, non-toxic and essentially free of sulfur and aromatics.
  • Safer to handle and transport
  • Fewer noxious emissions than petroleum-based diesel, and virtually eliminating acid rain-causing sulfur dioxide
  • Runs in any conventional, unmodified diesel engine
  • Improved lubricity
  • Renewable
  • Does not make substantial impact on foreign oil dependency

  • Production requires more energy than is produced after factoring in the energy required to grow the crops to turn into biofuel

  • The energy content of neat biodiesel (100% biodiesel) is about 11% lower than that of petroleum based diesel fuel, resulting in a power loss in engine operation.

  • Neat biodiesel and higher percentage biodiesel blends can cause a variety of engine performance problems including fuel filter plugging, injector coking (carbon deposits), piston ring sticking and breaking, elastomer seal swelling and hardening/cracking, and severe engine lubricant degradation.
  • Studies found injectors and pumps failing at around 50,000 miles with neat biodiesel. There is little information on the use of biodiesel with engine durability over the mileage and operating conditions of heavy-duty diesel engines.
  • Long-term storage problems occur from the poor oxidation stability of biodiesel fuels.
  • Biodiesel fuel at low temperatures can thicken and plug fuel filters.
  • Properly refined biodiesel tends to cost more than gasoline.
  • Diesel engines represent a small portion of the American car market.
  • Raising the right crops might cause deforestation.
  • It takes so much soy to produce a gallon of biodiesel, that the net GHG advantages are likely to be almost nil.
  • Agriculture with industrial fertilizers release some N2O unintentionally as part of nitrogen fertilization, and that nitrous oxide has a much stronger effect on global warming because it has a long lifetime in the atmosphere
  • Biodiesel is subject to microbial growth causing operation problems
  • Fuel system corrosion and premature fuel filter plugging.
  • Studies found increased nitrous oxide (Nox) emissions with higher concentrations of biodiesel.
  • Biodiesel fuel is very hard on your engine lubricant (oil).  The following detrimental effects are noted when concentrations of biodiesel exceed 5%:

    1. Fuel begins to dilute the oil resulting in a viscosity reduction

2.Increased sludge and varnish formation

3.Depletion of alkalinity reserve in the oil indicated by total base number (TBN) decrease

4. Certain metals such as copper and lead leached from bearings due to biodiesel fuel in the lubricant
5. Oil filter plugging from sludge
Alternative Fuel Definition: Pro's Con's
Any car with a battery-powered motor—including every variety of hybrid—is an electric vehicle to some extent. A pure electric vehicle would be run entirely by the battery-powered motor.

Electric-powered vehicles would be best for people who make a lot of short trips or commuters who drive frequently in traffic, since that’s when the battery-powered electric motor would be doing most of the work.



  • Benefits the Environment (Provided the Electricity is also generated from a "clean" source)
  • As with plug-in hybrids, electric vehicles could be cheap to fuel, given the relatively low cost of electricity drawn from the power grid through an ordinary outlet.
  • Power drawn overnight at off-peak rates could cost one-fourth the equivalent of gasoline.
  • Fueling from home could cost 80 percent less
  • Could help reduce approximately 450 million metric tons in greenhouse gas emissions a year by 2050


  • Requires specific vehicle - Can not be converted
  • GHG would be released by power plants that are supplying to the grid the electricity that are charging the batteries. 
  • Large battery packs take up extra space, add weight to the car, and degrade performance—and right now they’re too expensive and unproven for mass production. Batteries required for an all-electric car would be even bigger than those needed in a hybrid—so big that the car would need to be designed around the battery. For now, they’d be very expensive, too.
  • Once the battery charge is depleted, there’s no real advantage to an EV—since it has to run on a gas engine or some other power source.
  • There’s not yet an affordable battery that can handle the deep charges and discharges that occur under normal use
  • Lithium-ion batteries might work, but nobody has mass-produced one that’s safe, reliable, and potent enough for a car.
  • The infrastructure remains under-developed in much of the USA.


Alternative Fuel Definition: Pro's Con's
Cellulosic Ethanol   
Cellulosic Ethanol is found in plant cell walls and is the most abundant naturally occurring organic molecule on the planet.  This makes it a potentially limitless source of energy.
Ethanol burns cleaner than gasoline, producing significantly less GHG.  Even factoring in the amount of fossil fuel required to make it, the fuel still comes out cleaner than regular gasoline.
Ethanol produced from cellulosic material such as switchgrass or corn stalks is considered by many to be a better alternative to corn-based ethanol primarily because it doesn't rely on food crops to be produced.


  • Benefits the Environment
  • Switchgrass has been shown to produce 540% more energy than was used to grow, harvest, and process it into cellulosic ethanol, while reducing GHG emissions by 94% when compared to gasoline.
  • Ethanol yields on marginal land averaged 300 gallons per acre
  • Biomass left over after converting switchgrass into cellulosic ethanol could be used to provide energy for the distilling and biorefinery processes, further adding to the fuel’s net energy balance.
  • Cellulosic biofuel does not require fertilizers, pesticides, energy, and water to grow.
  • As a liquid fuel and it is much more compatible with our existing fueling system.
  • Requires vehicle fuel system modification
  • The cost of the enzymes needed to break the cellulose down is currently cost-prohibitive. 
  • Producing cellulosic ethanol on an industrial scale is too expensive
  • The technology doesn’t yet exist to mass-produce Cellulosic Ethanol
  • Cellulosic Ethanol can only offset a small amount of petroleum use.
  • The energy difference is significant:  1 ½ gallons of cellulosic ethanol = 1 gallon of gasoline.  Ethanol has two-thirds of the energy of a gallon of gasoline
  • Existing oil pipelines are not compatible with ethanol, so significant infrastructure spending would still be required if ethanol were to become the major transportation fuel.
  • The infrastructure remains under-developed in much of the USA.
Alternative Fuel Definition: Pro's Con's
Sugar Ethanol   
Brazil is the world's second largest producer of ethanol and the world's largest exporter, and it is considered to have the world's first sustainable biofuels economy and the biofuel industry leader.
In Brazil in 1988 vehicles running on 100% ethanol (E100) held almost 90% of the Brazilian‘s market, but a crisis in ethanol supply in early 1990 left thousands of vehicles out of fuel in their garages.
Sales of alcohol-only cars tumbled after this shortage coupled with low gas prices in the late 1980's to early 1990's
  • Benefits the Environment
  • Sugar ethanol can produce over eight times the amount of energy expended in its production (versus a 2:1 ratio for corn ethanol production
  • Ethanol made from sugarcane is more sustainable to produce than that made from corn.
  • Requires vehicle fuel system modification
  • There is abundant scientific evidence already that environmental degradation from soil erosion in sugar-cane fields is widespread
  •  With demand for ethanol soaring in Brazil, sugar producers recognize that it is unrealistic to think of exports to the United States now.
  • Over the longer term, the profitability of producing ethanol from sugarcane and sugar beets depends on the prices of these two crops and the costs of conversion
  • Sugarcane ethanol is a fuel additive that contributes only a few cents to the current price of American gas.
  • The infrastructure remains under-developed in much of the USA.
Alternative Fuel Definition: Pro's Con's
Corn Ethanol   
Ethanol produced from corn as a biomass through industrial fermentation, Chemical processing and distillation is primarily used in the United States as an alternative to gasoline and petroleum.
It is the most common type of Ethanol in the United States, but is considered less efficient than other types of ethanol (sugar cane, etc.) especially when only the vegetable itself is used and not the whole plant.
CO2 is released during ethanol production and combustion, but it is recaptured as a nutrient to the crops used in its production.
  • Benefits the environment
  • Corn ethanol produces 350 gallons per acre
  • It’s renewable
  • Corn is plentiful in the United States, making it a domestic resource.
  • Burning corn ethanol can cut greenhouse-gas emissions by as much as 20 percent, compared with gasoline.
  • Producing ethanol generates fewer emissions


  • Corn-grain ethanol typically uses gas or other power sources for processing.
  • Only displaces a small fraction of petroleum usage because it is blended with gasoline.
  • Contains 1/3 less energy than gas, which means mileage is 30 to 40 percent lower and costs are higher than gasoline as a result.
  • Massive ethanol production could cause a shortage of corn available for food and destroy habitat.
  • Cars must also be specially outfitted to run on E85.
  • There are no pipelines to major population centers.


Alternative Fuel Definition: Pro's Con's
The concept is similar to hybrids: an electric motor would drive the car much of the time. In this case, the motor would be charged by something under the hood called a fuel-cell stack, which converts hydrogen and oxygen into electricity that flows to the battery. The on-board fuel would be hydrogen.
Hydrogen could come from renewable sources and generates no tailpipe emissions


  • Benefits the Environment
  • Hydrogen is widely available.
  • The only tailpipe emission is water.
  • Pound for pound, hydrogen fuel has more inherent energy than gasoline, which could mean higher mileage: A prototype Honda fuel-cell vehicle gets the equivalent of nearly 70 miles per gallon.
  • If mass-produced and widely distributed like gasoline, the cost of hydrogen fuel could be equivalent to $2 per gallon or less.
  • Hydrogen could come from renewable sources.


  • Requires vehicle fuel system modification
  • While it can be extracted from water, currently the cheapest source of hydrogen is natural gas, a nonrenewable hydrocarbon.
  • There’s no distribution system or standardized method of storage, which is crucial since hydrogen fuel is a gas that must be kept under high pressure.
  • One enduring challenge is "cold start"— the ability to power up at temps as low 30 below zero Fahrenheit—which means fuel cells are ill-suited for the coldest climates. That may be resolved by the time other technology matures.
  • The infrastructure remains under-developed in much of the USA.


Alternative Fuel Definition: Pro's Con's

Methanol is the simplest alcohol chemically, containing one carbon atom per molecule. Commonly known as “wood alcohol,” it is a toxic, colorless, tasteless liquid with a very faint odor. Because it is produced as a liquid, methanol is stored and handled like gasoline. Most methanol is currently made from natural gas, but it can also be made from a wide range of renewable sources, such as wood or waste paper.


  • Benefits the Environment
  • Reduce hydrocarbon emissions by 30 to 40 percent with M85 and up to 80 percent with M100 fuels.

  • Potentially lower nitrogen oxide emissions due to a high heat of vaporization and lower peak flame temperature.

  • Forms no particulate matter when combusted; M85 will have some particulate emissions due to the gasoline component of the blend.

  • Lean combustion results in lower overall volatile organic compound emissions and higher energy efficiency.

  • Potentially greater direct formaldehyde emissions.

  • Reductions in indirect formaldehyde formation because the hydrocarbons emitted are less reactive.





  • Requires vehicle fuel system modification
  • The infrastructure remains under-developed in much of the USA.
  • No auto manufacturers produce M100 methanol vehicles

  • Highly toxic

  • Methanol is not volatile enough to be effective at starting an engine that is cold, but when it is mixed with gasoline this problem disappears.

  • This fuel is very corrosive, and because of this special materials and storage equipment may be needed.

  • Methanol does have a lower energy content than gasoline does, and there is also a higher cost ratio as well when compared to gasoline.


Alternative Fuel Definition: Pro's Con's
Compressed Natural Gas   
Natural gas is already one of the most widely used forms of energy today.

CNG vehicles generate fewer exhaust and greenhouse gas emissions than their gasoline- or diesel-powered counterparts by storing natural gas in high-pressure fuel cylinders at 3,000 to 3,600 pounds per square inch.
     The necessary infrastructure to support Natural Gas as an alternative fuel is already partially constructed and many of the components of the infrastructure are  exactly the type of infrastructure that will be needed to support another gaseous fuel, like hydrogen
  • Benefits the Environment
  • Available domestically today and offers an immediate impact on GHG, economical concerns and foreign oil dependency.
  • Dual fuel gasoline and CNG conversion kits are available to provide a transitional system as the infrastructure develops.
  • The United States has vast natural gas reserves distributed across the country through extensive pipeline systems extending from the wellhead to the end-user.
  • Home refueling is available
  • Natural gas requires little processing before use (unlike gasoline which requires the refinery process).
  • CNG has a significant emission-based advantage - producing much less CO and CO2 emissions when compared to gasoline at  a20% reduction.   Compared to gasoline burning it reduces carbon monoxide by 90 - 97%, nitrogen oxide by 35 to 60% and non-methane hydrocarbon emissions by 50 - 75%. Though not a renewable resource, natural gas is plentiful in supply.


  • Requires vehicle fuel system modification
  • Natural gas is a fossil fuel and is not considered renewable
  • There is a cost of conversion for vehicles to operate on CNG
  • Emits methane which is another GHG.
  • NGV’s are not as widely available in the United States as they are in other countries.
  • The infrastructure remains under-developed in much of the USA.
Alternative Fuel Definition: Pro's Con's
Liquified Natural Gas   
Liquefied natural gas, or LNG, is natural gas in a liquid form that is clear, colorless, odorless, non-corrosive, and non-toxic.
LNG is produced when natural gas is cooled to minus 259 degrees Fahrenheit through a process known as liquefaction.

Concentrations of hydrocarbons, water, carbon dioxide, oxygen, and some sulfur compounds are either reduced or removed.

LNG is also less than half the weight of water, so it will float if spilled on water.
Because of LNG's increased driving range, it is best used in heavy-duty vehicles, typically vehicles that are classified as "Class 8" (33,000 - 80,000 pounds, gross vehicle weight).
  • LNG offers an energy density comparable to petroleum and diesel fuels and produces less pollution
  • In most cases LNG is still superior to alternatives such as fuel oil or coal
  • LNG meets “the most stringent environmental requirements.”
  • Benefits the Environment


  • Relatively high cost of production
  • The need to store it in expensive cryogenic tanks has prevented its widespread use in commercial applications
  • Concerns over the safety
  • Because of the energy required to liquefy and transport LNG, the environmental performance of LNG is inferior to that of natural gas
  • LNG must be kept cold to remain a liquid, independent of pressure.
  • Requires vehicle fuel system modification


Alternative Fuel Definition: Pro's Con's
Liquefied Petroleum Gas (LPG) is a mixture of propane and butane.

The simple chemical make up of the gases ensures that they are clean burning.

LPG is produced as a by-product in both the extraction and refining stages of oil production.


  • Benefits the Environment
  • LPG cars produce 90% fewer particulate emissions and 90% less Nitrogen Oxides than diesel engines.
  • LPG engines produce 75% less Carbon Monoxide than petroleum and have 87% less Ozone forming potential.
  • If you spill LPG, it evaporates rather than soaking into and polluting the ground.
  • LPG engines run up to 50% more quietly than diesel engines.
  • Requires vehicle fuel system modification
  • No LPG-fueled light-duty passenger cars or trucks have been produced commercially in the U.S. since 2004
  • Propane poses significantly higher safety risks than gasoline. LPG is a “heavier than air” flammable gas at atmospheric pressures, which is not an ideal combination for a fuel with respect to leaks and spills.
  • It takes about 3 gallons of propane to equal 2 gallons of gasoline.
  • Not renewable.
  • LPG is generally higher priced than other fuel alternatives such as CNG and gasoline.