Unless you find a fast station that sells ethanol free gasoline (and you'll know because it costs more), gasoline is cut with up to 10% ethanol. 1 gallon of ethanol is equivalent to 2/3 a gallon of good old gasoline. So to keep things simple, if you buy 10 gallons of gasoline @ 20 mpg is 200 miles. But 10 gallons of gasoline with 10% ethanol filler is really 9.6 gallons, that's only going to get you 193 miles. That's a 3.3% loss. Probably not enough to account for your "much less" observation.
Now is right about the time that refineries and gas stations switch from winter blend to summer blend, so maybe there's something to that.
Do you always fill up at the same station or same brand? Maybe they are adulterating the fuel (higher ethanol content, etc.). You can get test kits for ethanol content. Maybe your vehicle needs a tune-up? They could also be fiddling with the dispensing measurement, saying that you put in 12 gallons, when it was really only 11. Harder to check than you might think, since some operators were adjusting things to come out correct at like 5 gallons, or whatever the local authority was using to audit things. Also, internal combustion vehicles get less efficient as they age/wear.
>I've noticed that I get much less gas than usual for the same number of bars.
I'm having a hard time parsing what this means.
>- gas smells less like gas
Is it possible for a person to smell the difference between octanes? The higher octane fuels have lower volatiles, so that might affect the smell.
Check your gas cap, I had this effect happen in my car because I had lost my gas cap. It can also happen in its damaged in some way. I don't have this habit so I can't tell you if I am observing a similar effect.
if you get into analyzing fuel samples beware that surprisingly small amounts of vapour can make a likewise large bang. just a drop or two of gasoline vapourized and ignited in a mortar tube, will make you change your pants.
I once read about a gas station that rigged their pumps. They discovered that the 'gas police' who came and measured gas to make sure pumps were properly working; always pumped a multiple of 10 gallons to measure.
They rigged the pumps to rack up more charges for the first 5 gallons, and then slow the charges for the next 5 gallons. That way it always read 10 gallons at those intervals, but overcharged you if you got less. Someone pumping 4 gallons (or 14) was charged as if they had pumped 6 (or 16).
They got caught when someone noticed that the gauge ran faster, then slower as you filled up.
Ethanol-doped gasoline (E0..E100%) has a lower BTU per gallon and a higher octane per gallon, assuming the same base fuel is used (e.g. 91 octane + E10 vs + E15). However, if manufacturers are cheapening the mix (e.g. 91 + E10 to 89 + E15) then they can hold the octane level steady while reducing your miles per gallon by about half the ethanol percentage (so, E15 is about 7.5% lower mpg vs. E0, or 2.5% lower mpg than E10).
You shouldn’t be noticing more than a 7.5% drop between E0 and E15 gas, which would be a pretty hard swing in gas composition. What % do your figures show?
Track it! Any Spreadsheet. Columns: date, where you filled up, how many gallons, dollar total, odometer reading, mpg function ((currentodo - prevodo) /gallons), ppg function (total / gallons).
You could also install something like https://lubelogger.com/ (naming decision aside), if you happen to do any self-hosting. It is a lightweight vehicle tracker. It has a fuel tracking screen. I personally only use it to track maintenance, but have been thinking about starting to track fuel consumption given the current disruption.
I did notice the MPG in a 2025 sedan with 19000 miles reading around 9–12mpg this week with a distance to empty of 170 on a full tank. It was more like 330, had been getting worse (200s) and now this.
And I have an old ford truck that absolutely wreaks of gas/exhaust or something rich when it’s keyed on now. Getting 9-12mpg in that thing wouldn’t get me to bat an eye but come on; in the new car?
Wasn’t doing this until I’d just filled it up last week. The last tank I went through was probably from February? I don’t drive it that much. You could say it has a pretty simple exhaust system that wouldn’t do as good of a job at masking theoretical adulterants. That didn’t even cross my mind, I just noticed this horrible noxious smell when I re parked it last night.
Los Angeles at the moment.
Didn’t California just lose a couple refineries who said no thanks and took a billion dollar loss rather than confirm to new environmental regulations?
Calculate volume and distance between the past twenty or fifty full tank fullups and then calculate distance ÷ volume for each of those pairs. If the number has dropped significantly, you’re getting fewer miles per gallon. If it’s dropped by a few percent starting five or ten days ago, it may be ethanol content (see E15 threads). If it’s dropped by more than ten percent, and has stayed there or worsened over multiple fillups, you may have a failing battery (which fucks up lots of car engine sensors) or a dirty/failing “MAF / AFR / front oxygen” sensor (which causes the car to mistakenly use too much gas). If you’re a thousand feet or more above sea level and your car has started taking longer to crank before starting at the same time, you may have a failing battery (see above) or a failing MAP sensor (which could cause the car to use too much fuel for your altitude).
Gasoline and diesel usually sell by volume, and if the temperature of the fuel is cold when you purchase it, you get more kilos per volume than you do when the dispensing tank is warmer.
There is quite a bit more expansion & contraction of hydrocarbons with temperature than many peoople expect.
In the US we're considering pounds per gallon rather than kilos per liter then ;)
Fuels containing a higher amount of Aromatic class hydrocarbons, (or just lesser "light" hydrocarbons) will have a higher density (lb/gal) compared to fuels having lower amounts of the heavier molecules.
Also the aromatics bring with them higher antiknock ratings which can also be better for efficiency in a number of different engines.
When acceptable octane rating is achieved by ethanol content instead, it works good too, but fuel efficiency is reduced chemically because alcohol does not consist of only carbon & hydrogen, alcohol molecules also contain oxygen which provides bulk but not energy, so alcohols can be considered to already be "partially oxidized hydrocarbons" to begin with. It's really the oxidation process of the burning fuel that provides the energy, and alcohols just have less to give than hydrocarbons.
Miles per gallon is the conventionally understandable measurement units, and even fuel injectors meter the fuel in by volume, but actual energy obtained and resulting engine efficiency depends on performance per weight of fuel, not exactly per gallon directly.
During changing seasons I like to feel the metal part of the gas nozzle for temperature during dispensing. One of the worst times is when a tank trailer has been sitting in the sun a while before delivery, and it's 95 Fahrenheit when it's not even that hot outside. I like it much better when a trailer comes from northern locations where the fuel is less than 60 degrees, then I buy more but don't fill it up. It's nice when it is colder fuel to purchase and if it's a hot summer once the gas warms up to ambient conditions you end up with more gallons than you pumped, but if you are not careful the gas tank will overflow "autonomously" if you fill it too much with cold fuel when it warms up like that :0
There are a number of other factors too, but this one is often overlooked.
Gas is likely mixed with cheaper Ethanol now. Depending where you live there's likely less taxes on Ethanol, too.
Ethanol has an Octane rating of 114%, meaning that you can run your engine with less fuel in the fuel/gas mixture, if your engine, pipes, fuel pump and rubber hoses are made for that.
Ethanol is pretty awesome in terms of HP output, but you have to reprogram the maps in the ECU to correctly use it. The timings of "how fast" Ethanol explodes inside your engine cylinders is also faster, meaning if you don't remap your ECU there's chances of backfire because the valves don't close fast enough. That means if you don't have a V-Tec or similarly digitally controlled valve steering you have to also modify your camshaft.
Source: Rebuild 3 cars and their engines to be fueled with Ethanol because I live near a race track with cheap access to Ethanol.
Edit: some gas stations in the past were using shitty additives to boost the ethanol mixture with toluols and methyl ethylene variants, so could also be that. They're really bad for your engine block. Like, reeeeally bad because their mixture is very unpredictable and varies too much for a proper ethanol ECU map.
Unless you find a fast station that sells ethanol free gasoline (and you'll know because it costs more), gasoline is cut with up to 10% ethanol. 1 gallon of ethanol is equivalent to 2/3 a gallon of good old gasoline. So to keep things simple, if you buy 10 gallons of gasoline @ 20 mpg is 200 miles. But 10 gallons of gasoline with 10% ethanol filler is really 9.6 gallons, that's only going to get you 193 miles. That's a 3.3% loss. Probably not enough to account for your "much less" observation.
Now is right about the time that refineries and gas stations switch from winter blend to summer blend, so maybe there's something to that.
Up to 15% in winter. But as xvxvx pointed out, they're going to extend it into this summer.
makes sense
Do you always fill up at the same station or same brand? Maybe they are adulterating the fuel (higher ethanol content, etc.). You can get test kits for ethanol content. Maybe your vehicle needs a tune-up? They could also be fiddling with the dispensing measurement, saying that you put in 12 gallons, when it was really only 11. Harder to check than you might think, since some operators were adjusting things to come out correct at like 5 gallons, or whatever the local authority was using to audit things. Also, internal combustion vehicles get less efficient as they age/wear.
>I've noticed that I get much less gas than usual for the same number of bars.
I'm having a hard time parsing what this means.
>- gas smells less like gas
Is it possible for a person to smell the difference between octanes? The higher octane fuels have lower volatiles, so that might affect the smell.
I love the smell of gas. It's weird. But I am def the type of person to notice a difference in smell.
> I love the smell of gas
There's a reason those molecules got the name aromatic compunds[1].
[1]: https://en.wikipedia.org/wiki/Aromatic_compound
Gasoline smells unhealthy, but mmmmm-asphalt.
Check your gas cap, I had this effect happen in my car because I had lost my gas cap. It can also happen in its damaged in some way. I don't have this habit so I can't tell you if I am observing a similar effect.
They’ve probably rolled out the E15 again:
https://carbuzz.com/feds-fight-gas-prices-easing-ethanol-res...
Now this makes a lot more sense. If the gov is allowing gas stations to cut with ethanol they are going to rob us.
there are things to check for water
https://bartovation.com/product/moisture-leak-detection/qual...
https://www.acustrip.com/cgi-bin/proddesc.cgi?s=40134
if you get into analyzing fuel samples beware that surprisingly small amounts of vapour can make a likewise large bang. just a drop or two of gasoline vapourized and ignited in a mortar tube, will make you change your pants.
https://thisvsthat.io/gasoline-vs-iso-octane
https://en.wikipedia.org/wiki/2,2,4-Trimethylpentane
https://www.waldeneffect.org/blog/How_to_measure_the_ethanol...
Check tire pressure. I had a prius and milage would drop significantly (60 to 50) when the tires were low.
Of course tune up.
Have you changed gas stations / brands recently?
I once read about a gas station that rigged their pumps. They discovered that the 'gas police' who came and measured gas to make sure pumps were properly working; always pumped a multiple of 10 gallons to measure.
They rigged the pumps to rack up more charges for the first 5 gallons, and then slow the charges for the next 5 gallons. That way it always read 10 gallons at those intervals, but overcharged you if you got less. Someone pumping 4 gallons (or 14) was charged as if they had pumped 6 (or 16).
They got caught when someone noticed that the gauge ran faster, then slower as you filled up.
Ethanol-doped gasoline (E0..E100%) has a lower BTU per gallon and a higher octane per gallon, assuming the same base fuel is used (e.g. 91 octane + E10 vs + E15). However, if manufacturers are cheapening the mix (e.g. 91 + E10 to 89 + E15) then they can hold the octane level steady while reducing your miles per gallon by about half the ethanol percentage (so, E15 is about 7.5% lower mpg vs. E0, or 2.5% lower mpg than E10).
You shouldn’t be noticing more than a 7.5% drop between E0 and E15 gas, which would be a pretty hard swing in gas composition. What % do your figures show?
Track it! Any Spreadsheet. Columns: date, where you filled up, how many gallons, dollar total, odometer reading, mpg function ((currentodo - prevodo) /gallons), ppg function (total / gallons).
You could also install something like https://lubelogger.com/ (naming decision aside), if you happen to do any self-hosting. It is a lightweight vehicle tracker. It has a fuel tracking screen. I personally only use it to track maintenance, but have been thinking about starting to track fuel consumption given the current disruption.
Maybe your tires need air or your engine needs a tuneup or it's windier.
Or not.
brand new tires and I maintain tire pressure
I did notice the MPG in a 2025 sedan with 19000 miles reading around 9–12mpg this week with a distance to empty of 170 on a full tank. It was more like 330, had been getting worse (200s) and now this.
And I have an old ford truck that absolutely wreaks of gas/exhaust or something rich when it’s keyed on now. Getting 9-12mpg in that thing wouldn’t get me to bat an eye but come on; in the new car?
Wasn’t doing this until I’d just filled it up last week. The last tank I went through was probably from February? I don’t drive it that much. You could say it has a pretty simple exhaust system that wouldn’t do as good of a job at masking theoretical adulterants. That didn’t even cross my mind, I just noticed this horrible noxious smell when I re parked it last night.
Los Angeles at the moment.
Didn’t California just lose a couple refineries who said no thanks and took a billion dollar loss rather than confirm to new environmental regulations?
Calculate volume and distance between the past twenty or fifty full tank fullups and then calculate distance ÷ volume for each of those pairs. If the number has dropped significantly, you’re getting fewer miles per gallon. If it’s dropped by a few percent starting five or ten days ago, it may be ethanol content (see E15 threads). If it’s dropped by more than ten percent, and has stayed there or worsened over multiple fillups, you may have a failing battery (which fucks up lots of car engine sensors) or a dirty/failing “MAF / AFR / front oxygen” sensor (which causes the car to mistakenly use too much gas). If you’re a thousand feet or more above sea level and your car has started taking longer to crank before starting at the same time, you may have a failing battery (see above) or a failing MAP sensor (which could cause the car to use too much fuel for your altitude).
Probably write your congressman to cancel all ethanol subsidies. It's an environmental disaster the EPA fell for.
Make sure you don't have a neighbor that's siphoning your gas at night.
I’ve been feeling this as well. I was wondering if something was wrong with my car. I used to refill once a month but I’m doing two refills a month.
Gasoline and diesel usually sell by volume, and if the temperature of the fuel is cold when you purchase it, you get more kilos per volume than you do when the dispensing tank is warmer.
There is quite a bit more expansion & contraction of hydrocarbons with temperature than many peoople expect.
I live in California. Our temperature variation is not that large to explain this difference in fuel efficiency.
In the US we're considering pounds per gallon rather than kilos per liter then ;)
Fuels containing a higher amount of Aromatic class hydrocarbons, (or just lesser "light" hydrocarbons) will have a higher density (lb/gal) compared to fuels having lower amounts of the heavier molecules.
Also the aromatics bring with them higher antiknock ratings which can also be better for efficiency in a number of different engines.
When acceptable octane rating is achieved by ethanol content instead, it works good too, but fuel efficiency is reduced chemically because alcohol does not consist of only carbon & hydrogen, alcohol molecules also contain oxygen which provides bulk but not energy, so alcohols can be considered to already be "partially oxidized hydrocarbons" to begin with. It's really the oxidation process of the burning fuel that provides the energy, and alcohols just have less to give than hydrocarbons.
Miles per gallon is the conventionally understandable measurement units, and even fuel injectors meter the fuel in by volume, but actual energy obtained and resulting engine efficiency depends on performance per weight of fuel, not exactly per gallon directly.
During changing seasons I like to feel the metal part of the gas nozzle for temperature during dispensing. One of the worst times is when a tank trailer has been sitting in the sun a while before delivery, and it's 95 Fahrenheit when it's not even that hot outside. I like it much better when a trailer comes from northern locations where the fuel is less than 60 degrees, then I buy more but don't fill it up. It's nice when it is colder fuel to purchase and if it's a hot summer once the gas warms up to ambient conditions you end up with more gallons than you pumped, but if you are not careful the gas tank will overflow "autonomously" if you fill it too much with cold fuel when it warms up like that :0
There are a number of other factors too, but this one is often overlooked.
gasflation
we are literally getting less of everything for more money. it sucks here
Gashittification
Gastrick Bypass
Gas is likely mixed with cheaper Ethanol now. Depending where you live there's likely less taxes on Ethanol, too.
Ethanol has an Octane rating of 114%, meaning that you can run your engine with less fuel in the fuel/gas mixture, if your engine, pipes, fuel pump and rubber hoses are made for that.
Ethanol is pretty awesome in terms of HP output, but you have to reprogram the maps in the ECU to correctly use it. The timings of "how fast" Ethanol explodes inside your engine cylinders is also faster, meaning if you don't remap your ECU there's chances of backfire because the valves don't close fast enough. That means if you don't have a V-Tec or similarly digitally controlled valve steering you have to also modify your camshaft.
Source: Rebuild 3 cars and their engines to be fueled with Ethanol because I live near a race track with cheap access to Ethanol.
Edit: some gas stations in the past were using shitty additives to boost the ethanol mixture with toluols and methyl ethylene variants, so could also be that. They're really bad for your engine block. Like, reeeeally bad because their mixture is very unpredictable and varies too much for a proper ethanol ECU map.