Gas cans do form pressure when subjected to heat or sunlight. The collapsing caused by cold tends to crease the plastic or metal so I usually equalize the pressure by releasing the cap. That may cause more pressure later but I can't say it has ever caused a problem. The key is to keep them out of direct sunlight and away from heat extremes.

I keep the vents open all the time except when transporting the cans to/from the gas station.

I'm sure I'm doing something wrong by venting vapors to the atmosphere or introducing air and moisture into the can. However, potential stale gas with a small amount of water in the can is far less of a problem than a failed gas can dumping 5 gallons of gas in my garage or shed. Maybe I'm rolling the dice, but I've never had a problem in 20 years of doing this. Some of the gas sits around for a year or more sometimes.

All of the gas tanks on my equipment or vehicles vent through the cap or some other means, so why not the gas cans too?

Hey Dave,

If I had a thief around, family or no, I'd fix him. Leave a gas can out with diesel fuel in it. It won't hurt his vehicle, but it'll cost him alot to have the fuel system purged. He can't say nothing to you because he was stealing it anyway.

Just dump whatever gas you have left in the can into your car/truck and then start fresh in the Spring (as long as it isn't two cycle mix of course).

Even leaving a "special" gas can sitting around in warm weather can be fixed up with some water on the bottom. The thief will smell gasoline in it, and when he pours it into his tank---well---gasoline from the pump will look a lot better after that. I met a guy who had two gas tanks in his car! The regular one, for the gasoline thieves, and one in the trunk to run the car on! He said the original tank worked well-he could tell by the cars in his neighbor hood that didn't start, nor run very well!
The regular tank had several gallons of gas in it, with several gallons of water for the gas to float on top of it!
When the thief did the first suck-up of "gasoline", thats what he got and tasted, but after that--------plain water!

yeah, i have thought about it but he is the kind that retaliate. last year while we were on vacation all we could think about was the gallons of plum jelly we would be making when we got home. the trees were loaded with large juicy plums almost ready to come off. got home and found not a single plum anywhere! he had come by and taken every last one while we were gone. my neighbor saw him over there, but thought it was ok since he knew who he was. i told him if he sees him on my property when i ain't there to call teh cops first and me second.

Right on rustyj. I like to tell the story related to me from a co-worker a few years back. It came to pass that one of the neighborhood kids in his area acquired a little "mini-bike". He and some of his friends (from about 8 years old to early teens) would ride this thing all around the subdivision where my friend lived. One day my friend was going to put gas into his lawn mower but his gas can was nearly empty. He said he "just knew" that he had filled that can 2 weeks before. Then his neighbor spotted him and asked if by chance he had been "missing" any gasoline lately. Yes, I have. Why do you ask? The neighbor related that ne had seen "the mini-bike kid" carrying a gas can down the street one night and that his own gas can was mysteriously emptying all by itself. They figured that the kid (or he and his buddies) were pilfering gas from the storage sheds in the neighborhood to fuel their toy. My friend "fixed up" a special "brew" and left it in his gas can. He put half water and half gasoline in the can and then put in a pint of some old shellac as a bonus. He said he checked it every day. Two weeks later, he noticed that half of the "gas" was gone. Two days after that he saw the kids pushing the mini-bike down the street. He said that they would push it a bit and then just "wear out" the recoil starter rope for a minute, then push it a little farther. That was the last time he ever saw the mini-bike. About two weeks passed and one day my friend was out in his front yard when he saw the kid that had the mini-bike ride by on a decrepit old bicycle. My friend asked the kid, "Why ain't you riding your mini-bike?" The reply was, "It quit running." My friend said, "If you didn't steal people's gas that wouldn't happen!" The kid said, "I ain't stole no gas from nobody." My friend said he told the kid, "Is that right? Then how come your mini-bike quit running?"

I just discovered that my two metal jerry cans with stored gasoline that I had in my backyard shed kind of swelled up a little due to probably extreme temperature of 116 F inside of the shed here in Nevada. They can't even sit straight I n the floor. I immediately took them out of there to my backyard covered terrace, where it's a few degrees lower at 108 F, but now I'm afraid of opening them to release the pressure inside and causing an explosion. What should I do? Thanks.