Previously, I wrote a few blog posts on how to "short" sell the oil companies as prices of gasoline increase. If you haven't read them, you can take a look at them here for some economics backrground of why this idea works.
I am reviving this discussion again because prices typically start to ramp up in the late spring for summer driving, and because I've been seeing Facebook posts telling everyone to fill their tanks full, among other things, to save money. You can view that article text here. There are a few reasons I don't agree with filling a tank full if you are driving only relatively short routes (around 50 miles per day or less). The biggest reason is explained in more detail in my previous articles, but briefly it has to do with "just in time" distribution. Energy distribution models today are highly efficient, and the distributors are counting on meeting certain demand numbers on average. Meaning they are expecting most people to fill their tanks full at each fill up, and will work to meet that demand. But, what if we change the demand from what they expect it to be? Remember supply and demand curves from your Econ class? There will be too much supply, and the price will go down until the curve reaches equilibrium again.
So, how can we do this? By not storing gasoline for the oil companies by filling your tank full and getting a 500 mile range of driving before having to fill up again. Instead, fill to half full or to a dollar amount that gets you somewhere near the half tank mark. There are plenty of gas stations around these days along most driving routes that making 2 or 3 stops per week will not make you lose much time. It might even save you from wasting time and gas idling at a red light if you stop at a station on a corner.
Another reason I don't see a need to fill to full unless driving a very long distance is that many tanks these days are 17 to 20 gallons. That's a lot of flammable fuel, first of all, and it isn't weightless either (meaning it does take energy to haul it around. Whether it is negligible or not is debatable). More importantly, cars that were much less fuel efficient in the 1950's and 60's had tank sizes around 16 gallons. If a tank that size was fine for a car that got 10 mpg fuel efficiency, why do I need to fill up with 20 gallons in a car that gets well over double the mpg's? If anything, 8 gallons should be fine. Something tells me they want us to buy more product for more revenue... kind of like how restaraunts have increased portion sizes so they can charge more, without you feeling completely ripped off. Fill to half full, and they'll think twice about their pricing models.
Yet another reason is that most cars these days have fuel pumps that won't be affected by low fuel levels, as long as you don't run out of gas. And they have built in screens to keep out any debris or settled material (which would end up at the bottom of the tank whether half full or not, which goes against the claims of the Facebook posts), and even then most tanks are built with very good materials these days that won't corrode easily.
Do you really need more reasons? Another reason is the widely used rule in investing of dollar cost averaging. Everyone knows you want to buy low, sell high. But how do you time it just right? Even highly trained professional traders get it wrong. Dollar cost averaging theorizes that if you just buy at smaller, more frequent, but evenly placed intervals, your cost basis will be better than if you try to time the market, or buy in lump sums (i.e., filling to full). Gasoline prices are volatile, and that is where dollar cost averaging by buying 2 or 3 times a week and filling only half full will help. This means that because you'll be filling at quite a few different gas stations along your many routes, you'll be averaging a better price than you would otherwise. And chances are you'll be able to take advantage of a "dip" in prices when you drive by that gas station with a ridiculously low price and you only have an 1/8 of a tank left, further averaging down your overall cost of gasoline.
Lastly, we all know it is human nature to conserve, or at least to remind ourselves to be more economical with, our goods when we see a limited supply. Hoarding, or in this case filling to a full tank, can lead to an increase in consumption just because of feeing comfortable in our bounty. Who knows, you may save two or three percent off of your weekly gas cost just due to the fact that you are more aware and keeping yourself from making unneeded extra trips because in the back of your mind, you don't want to have to stop at a gas station sooner than usual.
