It used to be the only number you had to worry about at the gas pump was the price.
But a new type of gasoline is rolling out across Wisconsin, and it is not for everyone.
The new fuel is called E15 and contains 15 percent ethanol, compared to the 10 percent in regular unleaded.
Though E15 is sold at the same pump consumers are used to, government warnings say it's not safe to use in every engine.
Joe Strazishar noticed the new fuel at an Oconomowoc KwikTrip earlier this summer and was confused.
"Number one, the name is very misleading," he said.
KwikTrip markets E15 under the name "Unleaded 88," a reference to the octane level of this blend of fuel.
On the pumps at KwikTrip, E15 is sold in the space that used to dispense 89 octane gas.
But "Unleaded 88" actually sells for a few cents less than the 87 octane fuel that comes out of the same pump.
The only thing explaining all this is a little orange sticker identifying "Unleaded 88" as E15.
"Their sign for 29 cent bananas is 100 times bigger than that 15 sticker," Strazishar said.
That warning label was created by the renewable fuel industry, which pushed for gas with a higher ethanol content.
The label was needed because E15 is not for everyone.
Nick Jarmusz from AAA Wisconsin said drivers need to do their homework before choosing the new fuel.
"You want to make sure you do your research and find out if it's approved for your vehicle. If it's not approved, you could be looking at some damage to your engine," Jarmusz said.
The orange warning label clearly states E15 is only for cars made after 2001.
But a warning letter from the Wisconsin DNR goes further, telling consumers to "consult the vehicle's owner manual to determine whether using E15 will affect its warranty."
Adding to the confusion is a federal law makes it flat-out illegal to use E15 gas in a list of engines.
E15 is off limits to motorcycles, buses and delivery trucks, off road vehicles, boats and snowmobiles, as well as yard tools like chainsaws, snowblowers and lawnmowers.
Joe Strazishar wishes KwikTrip had done a little more to help people like him understand the change.
While the company has been selling E15 for weeks under the name "Unleaded 88," it's still not ready to talk about it.
A spokesperson responded to a request for an interview by declining to talk about E15.
"We are still in the evaluation/testing phase, but feel like mid-September would be a good time to circle back."
To a confused consumer like Joe Strazishar, that's putting the cart before the horse.
"Consumers need to be prepared for that. They would have done a great service in actually doing it the other way around and say it's coming, it's coming," he said.
KwikTrip is not the only gas station rolling out E15 in Wisconsin, right now they're just the biggest.
The I-TEAM told KwikTrip when our story would air and asked for a chance to talk.
We never heard back.
Best advice: if you want to know if E15 is right for your car, call your dealer or mechanic.