Its promoters insist it is an environmentally greener fuel than straight-up gasoline, but that is debatable. Not for nothing are its biggest boosters corn farmers — for whom ethanol is a cash cow — while environmentalists are divided.

The Chicago City Council should reject an ordinance that would require the sale of a gas with a higher blend of ethanol at many service stations. The questionable benefits don’t justify the costs.

The proposal before the Council would require larger gas stations to install at least one pump that dispenses E15, a blend with 50 percent more ethanol than the gasoline now sold at pumps in the city. Supporters also say the industry would set aside $11 million to help service stations pay for the transition.

Today’s regular-grade gasoline is called E10, which means it has 10 percent ethanol, a biofuel usually made from corn or sugar. But alternative-fuels backers would like Chicago to be the first city in the nation to raise that to 15 percent. They say ethanol saves money, reduces American dependence on foreign oil and does less harm to the environment.

That position was supported last week by an analysis from Steffen Mueller, principle research economist at the Energy Resources Center at the University of Illinois at Chicago. It concluded Illinois could reduce carbon pollution by up to 663,646 tons per year by giving motorists access to such fuels as E15.

Under the ordinance, about a quarter of Chicago’s roughly 400 gas stations would be required to offer E15. The retrofitting would cost as much as $300,000 per station, and there’s no guarantee the $11 million  fund would cover those costs, according to the Illinois Retail Merchants Association.

Moreover, E15 can damage lawnmowers, snow blowers and other gasoline-powered tools, especially older models. It could invalidate warranties on some of the city’s 13,000 boats. Older cars, trucks and motorcycles also would be at risk. Auto companies say E15 would void warranties for many models, and not all models now coming off the assembly lines are compatible with E15.

Notices would be posted on pumps dispensing E15, but who is going to notice them amid the signs for diesel, regular, regular plus, premium, car washes and 99 cent coffee?

A bill in the Illinois Senate with similar provisions died last week, and a similar House bill is mired in committee. The City Council should be no more welcoming.