How much fossil fuel does it take to make gas?

Before I changed it, Wikipedia’s entry on Cellulosic ethanol (which is as likely a technology to save the world as there is) claimed that:

It takes 1.2 gallons of fossil fuel to produce 1 gallon of ethanol from corn. This total includes the use of fossil fuels used for fertilizer, tractor fuel, ethanol plant operation, etc.

This turns out to be incorrect (see below) and I have heard variations on the argument that “more than a gallon of fossil fuels are used to make the equivalent to a gallon of gasoline out of ethanol” in conversation and on television. It seems like they appear all over the web. While I find it to be a little surprising, at first glance it at least seems plausible. However, it begs the question — how much fossil fuel does it take to make a gallon of gasoline? That turns out to be an extremely tough question to answer. (Don’t get me started on how hard it is to try to figure out how much it costs to make gasoline — although this info from the DOE helps a little.)

If we are going to consider how much petroleum is used to make chemical fertilizer, transport the corn and ethanol, and even feed the workers involved shouldn’t we do the same for gasoline? After all, we have to dredge the oil up from the ground, often ship it halfway around the world in supertankers (anyone know know the fuel economy for a Suezmax tanker?), before refining it into gasoline. So I did some googling, and more googling, and even more googling to try to find the answer. This was difficult. On my second evening of attempting to sort things out I found a meta-analysis of various cost-benefit models for ethanol production that answered the question.

In the January 27 2006 issue of Science, Farrell et al. examined six studies of ethanol. (The paper, the meta-analysis framework used, and responses to criticisms of the work are all available on-line.) According to their research, it takes 1.1 joules (J) of petroleum (and an additional 0.09 J of other fossil fuels) to produce 1 J of gasoline. Since a gallon of ethanol contains less energy than a gallon of gasoline, the 1.2 gallons petroleum to one gallon of ethanol ratio should be devastating. Except that it is completely wrong. According to Farrell et al. the correct number is more like 0.05 J of petroleum, and 0.7 J of coal and natural gas (both of which are abundant in the United States) to make 1 J of ethanol.

The people (at least one of whom is a retired entomologist) who produced the 1.2:1 ratio seem to be more than a little off target. They also also claim that ethanol actually produces less energy than goes into its production. To arrive at this result, not only do they include factors like transportation and food for workers for ethanol — an analysis they do not repeat for gasoline — but they also ignore the energy gains from corn ethanol waste products. That might seem trivial, but when your waste products are protein and corn oil — two commonly used goods — the benefits are significant. By this sort of incorrect reasoning, one could argue that it takes 2.19 gallons of oil to make a gallon of gasoline because the rest is turned into things like diesel and jet fuels. It simply doesn’t make sense and it’s a shame that such a poor argument has made it out into the world and is now ammunition for people too lazy to do anything about climate change, sustainability or energy independence.

That said, the current means of producing fuel from plant matter only (begin to) address energy independence and sustainability concerns — if we produce enough fuel for ourselves then we don’t need to compete with other nations for a non-renewable resource nor do we necessarily need to try to stabilize questionable regimes in oil-producing countries. However, ethanol production from corn sugar does not seem to do much to help (and may even hurt) man-made climate change. And unlike ethanol from sugar cane, which yields eight times the invested energy in Brazil, corn sugar ethanol only returns a third more than the invested energy (gasoline gives six times the investment). So, there are many reasons that the current infrastructure for producing ethanol from corn is not ideal. Even Rolling Stone has an interesting take on the drawbacks of the current plans to produce ethanol.

In the end, the consumption of fossil fuel simply isn’t the problem with corn ethanol. That argument should go the way of the ether


6 Responses to How much fossil fuel does it take to make gas?

  1. This is an excellent article and well researched. Even if ethanol could be made at a 1:1 ratio(or less) with gasoline and even if a 1:1 ratio(or more) of energy output could be sustained, the one argument left unsaid is the amount of land needed to grow the crops. How many acres to produce a ethanol? One acre or less is out of reach if the amount of gasoline used is in the hundreds of millions of gallons. There’s not enough arable land to grow fuel.

  2. monado says:

    Excellent article. Just one little thing: it doesn’t beg the question, it raises the question. Begging the question is a rhetorical trick that assumes your conclusion, e.g. calling an embryo an unborn child.

    Like the “land bank” or feeding corn to hogs instead of letting the price go down and selling it to hungry nations or producing less, growing corn to make ethanol is just another subsidy on corn. Price supports on corn, milk, sugar, etc. are a way for all the rest of us to pay farmers to live in their chosen profession instead of doing something that makes sense economically. Sure, it’s nice to to keep “the family farm,” but that means the rest of us pay twice as much as we should for milk, sugar, etc.

    I’ll be linking to this from my blog.

  3. jwambaugh says:

    Land usage is an outstanding point that I hadn’t considered. Apparently there are about 400 million acres in use for farming in the U.S. right now ( The necessary water (and chemical fertilizers, often made from petroleum) to make enough additional land available probably isn’t there, so we’ve definitely got another reason that ethanol from corn sugars just isn’t going to work in the long run. There are some cellulosic ethanol test plants coming on-line in the next few years — that technology would certainly change the math.

  4. bmarts says:

    Slightly off topic, but I recently read an article from Nature that included a brief review of several photovoltaic (solar panel) technologies. It stated that 5 GJ (that’s Giga-Joules) were required to produce one square meter of the traditional Silicon based solar panels. This blew me away as, depending on the efficiency of the panel, you’d have to run it for 1-2 years just to recover the energy the used to make the darn thing. The article was from 2001 so it’s possible the 5 GJ number has been reduced since then, but the bottom line was that it’s expensive to make the Silicon based solar panels.

  5. jwambaugh says:

    Hey Brad — I just saw a talk on cellulosic ethanol research that is going on at RTI last week. Apparently things are moving along, but it may be decades before we can displace a meaningful fraction of the U.S. oil consumption.

    The cost of producing electric panels may not be as bad relative to oil as you think, though. I sat through “There Will Be Blood” Monday night and it had me thinking about all of the energy that goes into discovering and pumping oil out of the ground. I haven’t seen that included in any of the analyses of the relative costs of energy sources, but I would think it would be significant.

  6. Steve R says:

    Farrell also found that carbon emissions stayed about the same.

    Now its land use + no change in emissions.

    I still don’t see substantial benefits producing corn based ethanol.

Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Google+ photo

You are commenting using your Google+ account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )


Connecting to %s

%d bloggers like this: