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You pay a premium for premium, but that’s not necessarily because it’s better.

Ben Nelms/Bloomberg

My husband buys premium gasoline even though our two cars don’t require it. He thinks it’s better for the engines and gives us more power. When premium was more than $1.70 a litre here, it cost more than $15 extra to fill up my van with it. Is it really worth it, or are we just throwing money away? _ Elaine, Vancouver

You pay a premium for premium, but that’s not necessarily because it’s better.

In May, the average retail price for regular (87 octane) was $1.28 a litre in Calgary, $1.38 in Toronto and $1.59 in Vancouver.

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For premium (91 octane), it was $1.46 in Calgary, $1.58 in Toronto and $1.79 in Vancouver.

Knocking, or pinging, is when the heat in the engine causes the gas in the cylinder to ignite on its own before the spark plug can do it. You hear, well, a knock or a ping.

“This creates undue stress on engine components,” said Stephen Leroux, automotive professor at Centennial College in Toronto.

Higher-octane gas is formulated to “produce a slower, more controlled burn” and is less likely to ignite before it’s supposed to in a higher-compression, turbocharged engine, Leroux said.

While a few performance cars require premium, most just recommend it.

“Pretty much every vehicle is designed to run on 87-octane fuel,” Leroux said. “They will run just fine on it.”

If you’re driving on a really hot day and really gunning it, you might need to switch to premium − but again, only if you hear knocking, LeRoux said.

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And if your car’s owner’s manual says to use regular? Again, unless you’ve got knocking, don’t knock the automaker’s advice.

“Octane has nothing to do with making more power,” Leroux said. “The BTU rating of [regular and premium] is pretty much the same and that is the part of the fuel equation that provides more output.”

And in fact, because premium burns cooler, it could cause carbon deposits − the technical term is gunk − in engines that aren’t designed for it, Leroux said.

And those detergents touted in ads for premium? We asked oil companies − most either didn’t immediately respond or told us to contact the Canadian Fuels Association.

“Billions of dollars go into research and every company pretends they have the best additives,” said Carol Montreuil, the association’s vice-president. “Some even boost [detergents] in higher premium products to convince consumers that their additives are better that the next-door competitor.”

Ottawa requires all gasoline to have detergents to keep your engine clean — so you’re getting them in regular gas too. But the formulas are usually secret and vary by company.

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“To what extent are some better than others or the result of more research and hence more expensive?” Montreuil said. “I have no idea.”

Montreuil said consumers should “first and foremost” use what the manual recommends.

“If they decide to take a better grade because they are convinced their car is getting better fuel efficiency or better performance, who are we to tell them they’re wrong?” he said. “At the end of the day, it’s a decision each consumer has to make.”

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