In June the US Supreme Court rejected a challenge by the petroleum industry’s lobbying group to block the sale of E15 fuel, a mix of 15% ethanol and 85% gasoline. As a result, people who drive older vehicles or use outdoor power equipment (OPE) such as portable generators and gas powered compressors will soon have to pay more attention at the pump.

The problem with ethanol is that it’s corrosive to rubber and can damage hoses, seals and gaskets in older engines not designed for use with a gas/ethanol fuel mix. And ethanol bonds with moisture in the air, which can separate out, sink to the bottom of the tank, and clog fuel filters and in-tank pumps.

It’s hard to know when it’s okay to use E15 and when it is not. The auto companies changed he formulation of the affected parts so in theory, vehicles produced in or after 2007 should be compatible with E15 fuel. The EPA (which favors the use of ethanol) has certified vehicles made in the 2001 model year and later, and all Flex Fuel – capable vehicles to be E15 compatible. To further add to the confusion, warranties do not always cover vehicles against damage from the use of E15. GM and Ford say it’s okay to use this fuel in their vehicles starting with the 2012 and 2013 model years.

There is far less confusion about whether or not to use E15 in portable generators, chainsaws, power washers, and the like – don’t do it. OPE products are not designed for use with this fuel and trade organizations such as the Outdoor Power Equipment Institute and small engine manufacturers  warn against using fuel that contains more than 10% ethanol.

It will take a while for E15 to become readily available. There are 180,000 gas stations in the US and only 24 of them currently have the blender pumps required to sell the fuel. But E15 will likely be cheaper than E10 (the current standard) so there will be an incentive to make the switch.