It just seems like common sense for all automakers to put it on the left side so the driver can see it in the side mirror.
Same rant for phone chargers. They should all be USB connections.
Most of the cars (that I have come across) with a filler flap and a non-locking screw cap have a small solenoid which locates a locking pin in the flap when the car’s central locking is activated, to give a degree of security, although most filler flaps aren’t sturdy enough to stand up to being levered with a large screwdriver or bar.
I think it certainly is enough of a problem in many parts of the world where cars may be sold/end up that most manufacturers do something about it.
I’ve heard the following before: imagine some guy’s car sputters to a stop because he ran out of gas. And so he manages to pull over to the side of the road, and walks a mile or so up the road to a gas station, and walks back with a gallon of gas, in hopes of getting back to motoring along.
Should we put the gas cap on the left, where cars will keep zooming next to someone too stupid to keep from running out of gas in the first place? Or would you prefer it on the right, where he’s more likely to not die?
Odd have a VW and I can unlock the passenger side gas thingy from the drivers seat …
Same here in the UK - seems to work just fine.
Sadly, it’s not true - I’ve heard that some cars have an arrow indicating which side the filler cap is on, but that’s not universal either.
My car has a small arrow next to the fuel pump icon that indicates which side the filler cap is on.
I know that in the UK and Australia (old home, new home) the fuel pumps have nozzles on both sides so traffic flows through in one direction only. Having the filler caps on alternate sides allows for the pumps to have nozzles on both sides and therefore more cars can be filled up at any given time for a given size of forecourt. It always just seemed logical to me to have the caps on different sides or this system wouldn’t work.
My old Mazda 323 had a lever to open the cap just to the right of the driver’s seat (right-hand drive car), the cap was on the passenger side.
Most cars in the US market still have unlocked gas cap covers. Remote release of the gas cap cover is usually an option available, though, especially if you don’t get the very base model of a particular car. Remote releases are usually just a cable, but sometimes electric. Locked gas caps are common in certain markets where the take-rate on higher-end models of the same car is less common. Mexico is a good example of where the base model is very prevalent, and locked caps are an option.
It’s very difficult to siphon a modern gas tank; the anti-rollover valve gets in the way. You could probably insert a very narrow tube, but it would take seemingly forever. On the other hand, if they know you’re asleep, then taking 1/2 to siphon might be acceptable to gas thieves!
The thing is, every little feature “isn’t that expensive,” but when you add them all up, you’re talking hundreds of dollars per vehicle. In mass market vehicle manufacturing, saving less than a buck per car can be a big deal. How many people will pick a car with two fuel fillers over a competing model just because it has two fuel fillers?
I never thought of that…
My cars, all “merikan” makes:
AMC Hornet station wagon, 197x, (first car, bought used, nearly junk, don’t remember exact year), Right side.
Next 3 were all Dodge Omni 198x [8 and 9] (first bought new [88], next two bought used [both 89], because Dodge wasn’t making Omnis anymore, after 1990, and I REALLY liked them), Left side.
Not mine, but my mother’s, and I have been being her “driver” since around
2000, SATURN, don’t remember model, right side.
Chevy Cavalier, 2000, Left side.
Dodge Grand Caravan 2007, (current), right side.
During my childhood, I was Dad’s and/or Ma’s “gas-pump monkey”, several models, left, right, and centerline (as mentioned by a previous poster), behind the rear plate.
There hasn’t even been the slightest HINT of standardisation during my entire lifetime, even amongst american made cars. It probably is not going to happen, unless our Congressclowns mandate one or the other.
There were certain model years of the Jaguar XJ6 that looked like they had gas caps on both sides. (Look here, scroll down to the third and fourth pictures; gas caps just at the base of the C-pillar.) I’ve never owned one, but I can’t find any reference to it having dual tanks. For that matter, one of the caps may just be fore show; I wouldn’t put it past Jaguar during that era.
I don’t think anyone has mentioned the Corvette, yet. Some models had the fuel filler right in the middle of the rear deck, where the trunk lid would be.
Not here in the UK (where most of the cars are everything but American by manufacture) - most cars have either a flap that locks along with the central locking, or can only be opened by the lever inside the car, or they have a flap that can be opened with a finger, but a lockable filler cap.
Fuel is quite expensive here, so maybe the theft risk is higher.
I guess another possible purpose of the lock is to deter vandals from maliciously adding things (that are not fuel) to the tank.
I pay $6,70 a gallon… so a full tank of gas is worth about 140 bucks. Some people might be tempted, which is probably why I haven’t seen a gas cap that doesn’t lock since the 90’s.
Re: OP: I don’t think it’s standardized because gas pumps are two sided.
Re: Costco pumps: That design of hose is quite common. Many places have them. However, what seems to be ignored is that most places have long hoses with a little retractable line holding it up. Go to any gas station with a short-looking hose and pull the hose. It should stretch as far as a Costco hose. The high attachment design is decidedly better though for vans.
Re: gas cap/panel locks: Yes, they are to prevent theft. Back in the day before they were common, it was common to steal gas by using a siphon. Lockable gas caps came first, but then people ended up with their keys smelling like gas. The lockable panel became the standard. Early models had a lock on them instead of the interior button. However, neither was as effective as that little flip panel inside the actual nozzle holder.
The worst arrangement I’ve ever seen was on a 1959 Renault Dauphin I used to own. It was a rear engine affair and the gasoline filler cap was located in the engine compartment NEXT TO the radiator filler cap. Neither one was identified, IIRC. One of the worst cars ever manufactured and I owned one.
Here in NJ, where we don’t pump our own gas, it’s a pain in the butt to have my cap on the passenger side. When I pull into a gas station, the attendants go to the window on that side, but I don’t have power windows, which means leaning over to roll down the window across whatever stuff I’ve got on the front seat. Or waving the guy around to the driver side and coming off like I’m some entitled bastard who’s too good to roll down a window for him.
Plus, most of the other cars have their tanks on the other side, and I’ve pulled into many a gas station to find lines at each pump. But I can’t really get into any of those lines, because my tank is on the other side from everyone in line.
FWIW, my 2001 Pontiac Grand Am had the filler cap on the right hand side.
Was driving a dodge pickup the other day (not my personal vehicle), and the gas gauge just straight up had a little placard indicating which side the gas cap was on. Such a simple solution. 
I think a better solution than all this nonsense about one-way gas stations and mandatory gas cap side placement would be to just have tanker trucks roaming the highways, with a system designed between the trucks and cars so you can refuel while driving without all this nonsense about gas stations and pulling over during your road trips! I think a probe-and-drogue system would be easiest to implement.
All European built cars have the gas tank on the passenger side. It is due to safety reasons. They don’t want you to subject yourself to traffic passing you by at 80 mph+ as you put spare gas into your vehicle on the highway. The American made cars simply put the gas tank on the driver side due to convenience at the gas stations and with that disregarded safety all together. Cheers! 
My American made Ford has the gas cap on the right rear ( passenger-side) fender. So, not all.
Most of my Triumphs have the gas cap in the middle. The 7 and 8 are on the back deck, slightly to the right.
And my Porsche 911 cap is on the left.
Same for my Alfa Spyder.
And my MG TC, TD, and TF are on the left as well. The A, B, C and Midgets are on the right, though.
Come to think of it, my Fiat 124 Sport Coupe.
I’ll be visiting my cars this weekend, so I’ll have a look around!