The Atrium

The Atrium  has the Survivors collecting gas cans to fill a Racing stock car in order to escape the mall in a similar manner to Scavenge Mode. After starting an elevator to get down to the car the Survivors are immediately mobbed by hordes of Infected while trying to get gas cans. The amount of gas cans remains at 8 regardless of difficulty. The number of gas cans needed may change, dependent on the number of Human players in the group during online campaigns. In single player mode, the non-player Survivors will not attempt to fill the car up with gas due to the fact that they're protecting you from incoming hordes.

Walkthrough
In this chapter you start out in the safe room from the last chapter. Stock up on ammo and weapons and head out. After a short ride in an elevator the scavenge match begins. There are thirteen gas cans scattered around the atrium outlined in white. There is no time limit on this but Tanks will spawn in when you reach certain milestones. It is recommended for two people to search the upper levels and toss them down for a speedy match. Usually Tanks will spawn around the eighth gas can, the tenth gas can, and the thirteenth gas can so it is a good idea to stop and help kill the Tank or the Survivors nearest the car will be crushed. Also keep an eye out for Spitters who can destroy gas cans with their spit, but if this occurs the can will simply respawn in its original location. When the car is all gassed up the players must stand on the platform the car is on to enter the rescue vehicle.

Campaign
The Survivors start in a hallway with two bathrooms. Search these bathrooms, as they usually contain helpful items (IE pills, adrenaline, defibrillators). the hallways then leads out to an elevator on the top floor of the atrium, where the finale beings. Inside the elevator, Ellis will explain his plan of fueling up Jimmy Gibbs Jr's stock car, and driving it out of the mall towards New Orleans. The Finale starts when the elevator doors open.

Depending on how many humans or AI bots are playing, the Survivors will have to get a certain number of gas cans (IE 8 cans for two humans, 13 cans for four humans). In Campaign mode, there is one can on the first floor, six on the second floor, and another six on the third floor (in Scavenge mode, there are 3 more cans on the 1st floor). Be very careful not to accidentally shoot the cans, this will destroy them, creating a giant fire and causing you to wait for them to respawn. One popular strategy is to throw the more remote cans over the railings down to the first floor. this well lead to quickly fueling the car in one go once all the cans are on the first floor.

In addition, work in pairs instead of as a group when throwing the cans down to spread out the horde and make the process quicker; the horde is focused on the center of mass of the Survivors, and pairing up will spawn the horde farther away and in fewer numbers.

A tank will spawn when you have collected about half the cans. the bottom floor of the atrium is very open, so his rock-throwing ability can be very deadly if cover is not found quickly. Fighting the tank on the upper levels can also prove deadly, as he can potentially punch you off higher levels. Molotovs and bile bombs can be found all throughout the level, so do not be afraid to use them on the tank. If the Survivors are very desperate, they can destroy one of there fuel cans to light the tank on fire. This is not a completely good tactic, as they will likely have to go fetch the can again when it respawn.

When the amount of cans needed is collected, the Survivors simply need to all stand on the podium the car is on to escape the mall. If they have one can left to get, they should only pour it when all the Survivors are near the car, as the final can will trigger the horde when its poured.

The Survivors
The Survivors can use nearly the same tactics as in campaign mode. The only major difference is that human-controlled spitters will purposefully try to destroy gas cans dropped from higher floors.

The Infected
Boomers: When playing as The Boomer cause as much havoc as possible. Vomiting on those with gas cans could cause them to panic and drop their can. this could also lead to shooting the can. A popular strategy in this level is spawning and waiting either behind the car, or in the upper floor levels right behind it, waiting for Survivors to start pouring, and puking on them.

Chargers: DO NOT attempt to charge from a height, because you will fail. Attacking groups or loners, The Charger is always the best shot. There are a lot of straight hallways that the Survivors must travel through to get cans. Also, a charger can break through the glass railings on the upper floors while he's charging. If he manages to charge a Survivor off these ledges, it can cause incapacitation or death. Charging a Survivor while he/she is pouring makes an easy target for a charge, seeing as they can't move for a few seconds while pouring. the Survivor also drops the can, and can potentially be very far from the rest of the Survivors.

Hunters: Aim for those with gas cans, they will drop them directly next to you and any savior with a shotgun is sure to hit it. If a Smoker has somebody, pounce someone else, preferably the smoked Survivors rescuer. Also, if you stand on the fourth story ledge, just above the car, and you wait until a Survivor tries to pour a gas can inside, they are helpless for a 20+ point pounce.

Jockies: Aim for Survivors on their own, these can be easily dragged into the many closets where hordes spawn. When attacking groups, aim for Spitter goo or attack in a pair, one Survivor will take massive damage. Try to get Survivors that are pouring cans into the car, they are usually by themselves, plus they drop the can, which a spitter can easily destroy.

Smokers: Go to a high vantage point in the atrium and cause plenty of damage, remember you need to be able to run away and recharge. Alert a Hunter to pounce your preys rescuer and wait patiently. Smoking Survivors that are pouring is a great way to buy more time, separate the Survivors, and expose a can to be destroyed.

Spitters: Spitters are very valuable in this level, as they can hide in the upper levels and constantly spit on the car or any other high value target on the lower floors. Spitter goo can ignite dropped gas cans (the ones with orange highlights), this is an invaluable ability when Survivors are throwing down cans from upper levels, as this well greatly delay the time it takes them to recover more cans. There is a spot right above the car which can be used on scavenge and versus. Simply wait here and spit at those trying to fill the car, you do not need to aim much.

Tanks: Remember to use concrete for those pesky; fast Survivors. If on the second floor whack your opponent over the edges. Note: Tanks don't spawn in scavenge mode.

Scavenge
In this level you can use nearly the same tactics used in Campaign mode. Keep in mind that:
 * There are now 16 possible cans to collect. 4 are on the 1st floor, 6 are on the 2nd floor, and 6 are on the 3rd floor.
 * No Tanks spawn in Scavenge mode
 * All Survivors automatically start with a medkit, and pills.
 * There are 3 adrenaline shots on one of the kiosks in the safe area. These can prove invaluable, as you run faster and can't be slowed down while carrying the cans, can revive teammates quicker, and can fuel the car quicker.
 * There are usually multiple items laying around the can locations. (IE Pills, Motovos, and even Tier 2 Weapons)

Trivia

 * The stock car and its driver are likely references Dale Earnhardt Jr., a NASCAR Sprint Cup driver who drives the 88 car and Richard Petty who drove a Dodge Daytona and a Plymouth Superbird in 1969-70, respectively, in NASCAR with the characteristically huge spoiler and blue paint.
 * An Uncommon Infected is Jimmy Gibbs Jr. himself. He is said to have 1000 health and will spawn, though only once and very rarely, he is immune to fire and covers your screen with motor oil like a Mudman. The Survivors also have special lines when seeing his zombie.
 * Oddly enough, when stepping out of the elevator, you are told "Rescue is Coming, Defend yourselves!" even though you're required to fill up your vehicle.
 * Left 4 Dead did this as well, when you refuel the plane in Dead Air during the finale, it says "Rescue is Coming, Defend yourselves!" even though it's sitting right in front of the fuel tanker.
 * The Hazmat Infected do not spawn in this chapter.
 * Do not put gas in the car while being healed, this causes the game to freeze.
 * Interestingly, while in the glass elevator, Ellis will explain his plan to escape the mall which is to use Jimmy Gibbs stock car. Part of the plan is to "find the car" even though it is clearly visible from the elevator (as is the layout of the atrium).
 * It is never explained why there are gas cans around the Atrium, as there would never be any need to fuel the car.
 * It could be that the fuel was dropped by other Survivors the Infected killed before they could refuel the car.