America's ethanol experiment may be coming to an end. Lawmakers on both sides of the aisle are calling for an end to the $6 billion a year ethanol subsidy.

The question is, if Congress does abandon ethanol, who benefits?  

One potential winner is other alternative energy sources. Cars now consume an astounding 25% of all corn grown as a result of the ethanol subsidy. But with ethanol out of the picture, other energy sources will be called upon to fill the void. Natural gas and electric vehicles are the most attractive options.

Congress agrees and is considering legislation favoring both. Many companies stand to benefit.

Electrifying investments
A123 Systems (Nasdaq: AONE) makes batteries for electric vehicles. The company has negative earnings, making it purely a story stock at this point. But the story is intriguing.

The company recently built the largest lithium-ion battery factory in North America in anticipation of federal support for the industry. If electric is the future, A123 Systems is in a good position to capitalize.

NRG Energy (NYSE: NRG) will charge the batteries that power electric vehicles. The company plans to construct a network of charging stations in major metropolitan areas across the country. Many of the stations will be available at popular retailers such as Best Buy. Of course, NRG Energy will charge for a charge. The estimated fee is $49 to $89 dollars a month.

Unlike A123 Systems, analysts expect positive earnings from NRG Energy this year, making it a safer electric vehicle investment option.

Natural investments
Westport Innovations (Nasdaq: WPRT) and Clean Energy Fuels (Nasdaq: CLNE) are two ways to play the natural gas transportation trend.

Westport Innovations holds proprietary technology enabling trucks to operate on natural gas. Clean Energy Fuels provides the stations to fuel the trucks. Both companies operate in the red at this point, but that could soon change if Congress passes legislation to jump-start the industry.  

The bottom line
Congress is searching for ethanol's successor. Natural gas and electric are the likely choices. Look for stocks in these industries to perform well in the near future especially with federal support. 

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Fool contributor Adam J. Crawford does not own any shares of any company mentioned in this article. Motley Fool newsletter services have recommended buying shares of Westport Innovations. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.