I used to go out of my way to find the cheapest gas but after running the numbers I found that the money saved just wasn’t worth the hassle.
Drive 15K miles per year in a car that gets 25mpg and you’re using around 600 gallons per year. Even if you could consistantly save 10 cents per gallon over the other guys you’d net a measly $60/year.
For the convenience of filling up when I want and where I want I’ll pay the $60 annual fee.
I’ve heard this since I started to drive, and I’ve never believed it.
It simply doesn’t make any sense at all - if the sediment is heavier than gasoline, it will be sucked up by the pump immediately.
Now, I could believe that if the gas was contaminated by something that floated on it, it would be more likely to clog the pump when the fuel level was low. But that’s not the scenario that anyone ever posits.
I buy as a hedge against disaster (earthquake, fire or other event that would cause evacuation), so I never let the car get below a half tank, which means price is irrelevant. The few pennies I would save by shopping for prices isn’t worth it to me. You all might try looking at it that way also, as it pretty much ignores price fluctuations.
I agree about not going out of your way. But I was addressing the situation in the OP where the driver does not go out of his way, and the only difference between strategies is time in the station. Your analysis of costs still applies, but as has been mentioned you have the risk factor that gas prices will continue to decline and you’ve spent extra time filling your tank with gas that is more expensive than you’d get if you had waited.
My father was right as usual. I get very nervous when the gas is low myself.
I would disagree as well. Sounds like an urban legend to me. What does Snopes say? 
Seriously, though, if the pickup is sitting right at the bottom, it’s going to pull in anything sitting on the bottom as soon as it gets there. If it’s off the bottom, it’s not going to pull it up at all. Even so, at worse, you’ll clog the filter. It shouldn’t get to the injectors.
Anecdotal data point: because of my lazy nature, I often wait until the tank is nearly empty to fill it. Never had a problem, even the time in west Texas I completely forgot to fill up and didn’t notice how long the gauge had been on E. It is my belief the car was running on good karma, because I don’t think there was any fuel in there! But I never had any problems with sediment.
Costco members save about 30 cents on gas per gallon this week. So I fill when going to Costco. Anything else, I just keep a price on numbers and try to keep the gas above half full. No amount of money savings is going to make up for running out of gas at a very inconvenient time.
You never want to run out - that’s would negate all savings.
It’s a myth about filling when it’s cold - underground tank temperatures don’t vary much (that’s why we store wine and cheese in caves)
When I was a fleet manager we tested a number of fuel saving devices - you may recall the magnetic ones and the ones that sprayed mist - and in every case the fuel consumption improved.
The trouble was that we found a similar improvement on the control cars not fitted with the device. The simple conclusion was that it was the monitoring that had the effect, not the devices. The lesson was that the best fuel saving device and the most effective fuel saving strategy is simply to drive as if you are a chauffeur. Think Driving Miss Daisy and you get the picture.
BTW - I feel really sorry for you poor guys paying what - nearly $4 a gallon, over here we pay £1.30 a litre which I approximate as $7.91 per US gallon.
There are people who’s job it is to track all that information for companies that refine and distribute gasoline. They have experience and easy access to all the relevant information as a matter of routine, You’d need to be able to second guess them and react faster than pricing changes arrived at the pumps…
That sounds like a lot of opportunity cost for small returns.
I did the pump jockey thing back in high school, at least until I was promoted to apprentice grease monkey 
The place I worked for was affiliated with one of the major oil companies. From what I saw, said oil company would send out a minimum price per gallon for each grade. The station could go a bit higher based on what the other nearby stations were charging, but the difference was usually less than a few cents per gallon.
and it’s not like this is all that lucrative for the gas stations. The markup on a gallon of gas is like 5-10 cents. They need to make their money on the attached garage, or the convenience store inside. It’s practically impossible to make money doing nothing but selling gas.
I have a friend that drives big vehicles with 20 gallon gas tanks, and never lets them get below 3/4 full before he fills up. He also doesn’t drive much these days. The fellow has to have some seriously old gas in those tanks, and I wonder if he ever has problems others claim happen form burning old gas. However, I also wonder if the problems others say come from burning old gas ever really happen, as long as it’s not a twenty-year old tank of gas in a barn-find car.
I’m with these guys.
Of all the vehicles I own, I think the biggest single tank is about 22 gal, so at 10 cents a gallon more at station X, I only spend an extra 2 bucks or so.
The cheapest place is the one closest to my house anyway.
I was rolling into Bishop, CA a while back, and the Indian Casino has the cheapest gas by about a few cents, but you gotta wait about 10 minutes to get a pump. Screw that! I’ll pay the extra and drive down to Giggle Springs and get the hell out of town that much faster.
As already mentioned it’s just about impossible to consistently save money by predicting the timing of price-at-pump fluctuations, so you must get your fuel savings by looking at time and price-difference-between-stations.
I checked into this for myself recently since my job has me driving over 37,000 miles per year, at my own expense. I drive a small VW, and keep very close track of the mileage in a log and constantly updated XL table; my records are precise enough that I can even tell when my wife drove the car in a given week due to the difference in mileage (she’s got poorer driving habits than me).
You may be able to prove on paper one way or another the effects of carrying different fuel masses, having the radio on, taking a leak before you get in the car to reduce weight, wind speeds at different times of day, etc. However, these cost factors are either beyond your control or are negligable; by far I’ve found the biggest savings factor to be distance and time you go out of your way to refuel. A big chunk of that is the cost of your time; I use half my hourly wage as the value of mine… if by chance a person places no value on their time or considers driving around after work trying to save money a hobby, then the rest below won’t really apply.
There are two factors in saving money on time spent: extra distance off your normal route to get to a particular gas station, and how frequently you drive there to refuel. If you are refueling twice a week and drive more than 4 miles beyond the nearest gas station to get to another with a lower price, it’s pretty well impossible to save money considering any realistic price difference you’ll find (you’d need at least 30 cents per gallon to break even). It takes time to get there and back plus burning extra gas in distance, so picking a nearby gas station is usually better even if it’s a bit more expensive. You can significantly improve further on this by refueling as infrequently as possible. I carry enough jerry cans to get 25 gallons more than my tank can hold (11.5). This way I only have to drive to the station to refuel every 12 days or so. I still have to put that gas into the car 2x per week, but it’s a lot faster to grab a jerry can from the shed than to drive to and from any filling station. By driving to the station infrequently, I save at least 68% when filling stations are close to my route and price differences between stations are big. If the stations get further away and the price difference is low, I can save over 50 times as much.
The numbers I came up with surprised me in a few ways, and can be counter-intuitive. Even with the numbers right in front of me I find it hard not to drive across town to take advantage of “cheap” gas. Part of that is because of what I refer to as the 5 minute delusion; a problem that plagues us all. That is, the knee-jerk reaction that “X task only takes 5 minutes” so time isn’t a factor… but it is. Anyone who can start slowing down, make a turn, drive 2 blocks, pull into a station, park, get out, open the gas cap/put the handle in, start the pump, pump their gas, replace it handle, cap back on, pay for the gas, start the car and pull out, get back on the road, drive the 2 blocks back, wait for traffic, pull out and resume the speed they were at before starting the whole thing in only 5 minutes is a magician. Most people spend 2-4 x as much time as they think they do on menial tasks like this, so don’t overlook it.
It’s great if you can get cheap AND convenient.
I go to the gym 4-7 times a week, depending on the time of year. The cheapest gas station in our area is right on the most direct route between the gym and my house. It’s also on the most direct route between my house and the nearest supermarket.
“Going out of my way to get gas” literally means turning off the street and parking next to the pump.
Having a cheap station right on your route is about as good as you can get, and if going there is part of a personal trip already, the extra time probably isn’t a big deal. It also depends on the type of roads you’re on and how busy they are; see below.
In my case the closest station to my route off a major 4 lane highway takes 6-8 minutes to get to as you have to take an overpass, drive a couple miles, go through a set of lights, and then through about 5 stop signs at max 15 mph in a maze of interconnected parking lots which are always busy… then 10 - 15 minutes to gas up as there is always a line (Costco with a pretty good price). Stopping off for gas takes me half an hour, and I don’t really have an option as to when I can go (plus I have the added bonus of not having any stations in the tiney hamlet that I actually live in). Due to my drive time I end up with about 4 hours per day to spend with the family… so saving time becomes a big deal for me.
Unless there’s a trend of rising or falling prices over time, then it’s more or less a roll of the dice, and the best you can do is to use something like Gas Buddy to identify the cheapest gas when you need it.
That said, if you watch a site like Gas Buddy often enough, you’ll get a feel for when gas is cheap, and you can go fill up at a half-tank, and then ride out any transient spikes if they occur.
So what are the optimum strategies if you do have a trend of rising or falling prices? My intuition tells me that what you want to do is fill up as infrequently as possible as the prices rise, and as frequently as possible as prices fall, but I may have that backward. Anyone actually done the math on that?
Gas prices are not random here, and have not been random for a very long time, if they ever were.
When I was young, we were on a cycle with a sharp rise and slow fall, about 10 days long, but variable.
A couple of years ago, we were on a fixed weekly cycle. Top on Wednesday, slow drift down to Bottom on Tuesday. This lasted long enough so that many people noticed (but not my wife), and there were lines buying the Tuesday night gas.
The big gas companies were able to take advantage of this by adding more pumps and lanes, so they captured even more of the market, and squeezed out the last few independents. Having done that, “Big Oil” teamed up with “Big Supermarket” in a coupon scheme, which squeezed out most of the last small chains, and shifted a lot of the demand to Weekends/Monday (after you’ve done your shopping and have your coupon).
Having done that, the competition isn’t as strong, which reduces the price swings, so we have gone to a cycle that is about a month long, with a long flat spot at the bottom.
I buy small amounts in a falling market, then full tanks at the bottom. I don’t pick the actual up corner now, I just minimise what I buy while I can see the price falling, then when the price flattens out I’ll get a full tank.
The peak is usually easier to pick than the minimum. If you use the strategy,
“ALWAYS buy after the price goes up” (as my wife did), then you get the worst possible result.
If you “always buy the minimum possible amount”, then you get the average prices, which is better than worst, but not as good as optimimum.
If you “always buy a full tank at random intervals” then you get the average price, which is better than worst, but not a good as optimum.
If you “NEVER buy a full tank at or just after peak price”, then you do better than average, and much better than worst.
If the minimum day is not exactly predictable, optimum strategy is to fill up on the last day you are sure of, then as much as possible every day after until the price goes up, then as little as possible until the price goes down.
Let’s say you get it right 9 times out of 10, and save $5 9 times: on the 10th time you save zero. Total savings $45 Then you push it a little harder, and 8 times out of 10 you save $6: on the other two times you save zero. Total savings $48, but you’re twice as stressed.
Then you push it a little harder, and save $7 4 times, and zero 6 times: total savings $28. You aren’t stressed anymore, because you stop trying.
Conclusion: Don’t try to guess the minimum, unless you have a gas station that changes late, it’s too much stress. If you can, buy before the minimum, otherwise just don’t buy at the peak.
Saving $5-7 on a single fill-up? Seems pretty damn unlikely. Even for a 20-gallon tank, that represents a swing of at least 25 cents per gallon. Sorry, but i’m skeptical that the price fluctuates that much on anything like a regular basis. It certainly doesn’t happen around here.
Here’s a chart for historical retail gas prices:
It looks like maybe there are 5-10 cent swings where I live (Dallas) on something approaching a monthly basis, but they get plowed under when there are major oil price changes going on.