Living in Iowa, it’s hard to avoid conversations about ethanol. And working for an advertising agency that previously represented the ethanol industry and continues to represent ethanol-related businesses causes the topic to come up in conversation for me more often than for the average Iowan even. I use ethanol in my car, as does most anyone who hasn’t put much thought into it. It’s commonly six cents cheaper. Who wouldn’t go with six cents cheaper?

Well, I’ve talked to a few people who wouldn’t go with six cents cheaper. Their logic comes down to efficiency. While ethanol is cheaper, it actually takes your car more ethanol to produce the same amount of energy, so you’re getting few miles-per-gallon with ethanol vs. standard unleaded gas. “Meh,” I told myself, “that’s a worthwhile tradeoff for a cleaner planet.” Then the ethanol dissenters typically suggest that the process of creating ethanol actually creates more pollution. After a few of these conversations, I decided to do some testing and find out the truth by the numbers.

82% of statistics are made up, so I set out to make up my own, in the only context that matters to me: my own car, a 1997 Buick LeSabre. Lacking the resources to test the pollution from my car (much less the processing plant at which my ethanol was produced), I decided to test what I could: the fuel efficiency of ethanol. Over the past couple months I’ve been recording all of my gas purchases, as well as my mileage between them.

The process of figuring out miles-per-gallon was actually a bit confusing to me at first, so I’ll explain it here. When I fill up my tank, I reset my trip odometer. On my next refill, I know how many miles I’ve gone while emptying my tank, and the amount I put in to refill the tank is equal to the amount of gas I must have used while traveling those miles, because a full tank is always the same size. So by dividing those miles by those gallons, I have a miles-per-gallon number.

This gets confusing when testing different types of gas, because the number of gallons on my current fill-up is actually the number of gallons used with the previous fill-up’s type of gas. I repeated this process several times, and attempted to get as close to a full tank as possible to avoid the previous tank skewing the efficiency of the current tank as I switched back and forth between 10% ethanol and 0% ethanol unleaded gas.

So that’s my methodology. Here are the numbers:

Ethanol % Gallons Miles Highway/City Miles-per-gallon
10% 15.056 393.7 Highway 26.149
0% 15.488 359.2 Highway 23.192
0% 14.571 257.0 City 17.637
0% 15.813 416.6 Highway 26.345
10% 14.923 370.3 Highway 24.814
0% 11.318 293.5 Highway 25.932
0% 16.497 371.0 City 22.488

Notice that I added a Highway/City driving variable to the data. I quickly noticed that my numbers weren’t nearly as steady as I was expecting, and I believe my hunch that this variance is primary due to highway vs. city driving is borne out by the numbers above. So the first conclusion is that any variance in efficiency between ethanol and non-ethanol gas is much smaller than the variance between city and highway driving. Those of us concerned about fuel-efficiency need to be working to make our cities more hospitable to walking and biking more than we need to be debating the merits of ethanol. Nonetheless, on to debating the merits of ethanol.

It’s clear to me from the numbers above that ethanol is indeed less fuel efficient than non-ethanol gas in my car. However, the difference is very slight, and it is more than offset by the standard price difference of six cents per gallon. Figuring that in, the average miles-per-dollar figures (for highway miles only, as I’m still finishing my tank of city-driving ethanol) are: 12.74 for ethanol and 12.21 for non-ethanol. So despite the lower fuel efficiency of ethanol, the price difference means that for every dollar I spend, I’m going more miles by using ethanol in my car. With this in mind, I intend to continue using ethanol.

But what about the pollution? Well, I’m not sure about the pollution. I haven’t seen any actual numbers on that, so all I have to go on is what other people say they heard somewhere. Some people say ethanol is better than non-ethanol gas for the environment overall (notably a former client of my employer says this quite often), while others say it’s worse. If anyone has any numbers on this, I’d be interested to see them. But lacking any testable numbers, it seems to me everyone is just arguing whatever reinforces their own beliefs.

And yes, I’m aware that dark forces (e.g. Archer Daniels Midland Company) are at work making corn an artificially prominent part of the American (and increasingly world) economy in everything from ethanol to high fructose corn syrup to construction materials. And maybe when I’ve finished reading Omnivore’s Dilemma this will be enough to convince me to act against my own immediate economic interests. But for now, I’m sticking with the six cents cheaper at the pump and the half a mile-per-dollar more on the road I get with ethanol. As the standard disclaimer says, your mileage may vary, and I’d encourage everyone to do their own testing in their own cars.