Left 4 Dead 2

It popped for me last night on the 15th canister that the team put into the car. You do not have to be the one putting the gas into the car, once 15 are in it pops for the whole team.

This achievement became easy on NoMercy - rooftop map (DLC Sacrifice), because there are 21 gas cans and get 15 of them will be simple.

There is an update that adds AI Special Infected to Scavenge, so if you haven't updated yet, don't do it because it will make this harder to get. Only special infected can make you drop a gas can.

Some tips: Use adrenaline, it makes you run faster and fill up the gas tank faster. Throw as many gas cans down to the ground as possible before you pour them all in, but make sure you have enough time to reach the gas cans from where you are. Each gas can adds 20 seconds to the time, even when you go into overtime, so don't worry if you go into overtime as long as you are holding a gas can, you should be fine. Try not to shoot the gas cans as they will explode, often destroying the can next to them, and you only have 16 to begin with. Using melee weapons is recommended to avoid accidentally shooting the gas cans.

It is best if you do it on Dead Centre since it is a smaller map and the cans are therefore closer together and more easily reached. This means you can throw more towards the centre and reach them quickly to fill the gas tank.

simply have another teamate run around and throw the gas cans to you, or have someone hold on to one causing overtime while you collect them. note gas cans are only collected after pouring them.

I did this by myself with a second controller, I just left the second controller sit their and collected gas cans. It took me 3 times to get 15 cans. The trick is to get all the ground level cans first and stack them next to the car. the run upstairs left or right doesn't matter and throw 2 cans down to the ground floor, more if you have time. Make sure you have a can in your hands when time get to zero. go to the car and put all the cans in the car. go back upstairs and throw as many cans down to the ground floor as possible and make sure you have a can in your hands when time goes down to zero again. put all the cans in the car again. repeat till you get 15 gas cans in the car. You can grab a shot at the beginning to give you a few extra seconds of time. I did this without the update that causes extra special infected in scavenge mode , at least I Heard the update makes it impossible to solo this achievement , not sure though. If you don't have xbox gold like me , this is the best way to get it in my opinion you can do this with a system link game also if you need help to get the 15 gas cans. If I can do it anyone can. good luck.