Can you explain the concept of old gas? How can gasoline age? How long does one store it before it is considered old? I have gasoline from last summer and have been afraid to use it in my new lawn mower because the instructions say I shouldn't use old gas. Considering the price of gasoline, I sure would like to use it. What am I supposed to do with it if I can't use it? I can't imagine it would be a good idea to dump it anywhere.

Can you explain the concept of old gas? How can gasoline age? How long does one store it before it is considered old? I have gasoline from last summer and have been afraid to use it in my new lawn mower because the instructions say I shouldn't use old gas. Considering the price of gasoline, I sure would like to use it. What am I supposed to do with it if I can't use it? I can't imagine it would be a good idea to dump it anywhere.

— Judy B., Medford

We searched for experts high and low from our fabulous Since You Asked headquarters. We passed this one by the Department of Environmental Quality, the Oregon Department of Agriculture Weight Measurement Standard staff and a chemist who tests gas quality for the state of Oregon.

But none of them could tell us exactly what the meaning of "old gas" is.

Rob Reed of Inspectorate, a laboratory that tests fuel quality in Vancouver, Wash., said gas will go bad eventually, but it could be three months, six months or two years before it happens. It all depends on the type and quality of the original gas.

"It doesn't mean it wouldn't combust in an engine," Reed said. "The question is whether it would make the engine run."

Next, we tracked down Ray Smith at Garris Environmental, a recycling company on Industrial Circle in White City. Smith knows bad gas when he smells it.

"You can really tell when it goes bad, because it smells like turpentine," Smith said. "If you left the gas in the mower all winter, it's probably starting to sour."

Garris Environmental doesn't charge for disposing of old gas in its tank, but if you're dropping off a container there is a charge It costs $3 to rinse and dispose of a larger can, along with a $3.50 state environmental fee. For a one-gallon container, it's 50 cents, plus the $3.50 state fee.

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