Scavenge Mode

"Haul ass and get gas!"

- Coach

Scavenge Mode is a competitive gameplay mode released in Left 4 Dead 2. It is a round based game in which Survivors attempt to find up to 22 gas cans to refuel a generator (or car), while fighting against player-controlled Special Infected much like in a Versus game. Before a game starts, the host can choose the amount of rounds to play (1 round, 3 rounds, 5 rounds).

Gameplay
Each round of a game consists of two turns. One team plays as the Survivors and the other plays as the Infected. When the turn ends, the teams switch sides. At the start of a round, the Survivors spawn next to the generator and will have 30 seconds to set up and grab their supplies, while the Infected find locations to spawn. The timer will start and the Infected will spawn as soon as the set-up time runs out or if a Survivor leaves the designated area around the generator. Once the game starts, the Survivors have 1 minute and 30 seconds to find gas cans, with an additional 20 seconds added for each can they bring to the generator. When the time runs out or all the Survivors are incapacitated, the teams switch sides. Next turn, the previously Infected will become the Survivors and will have to get one more gas can than the other team to win the round and end it. If both teams collect the same amount of gas cans, the team that did it faster wins the round. In the case that both teams do not collect any gas cans, the round goes to the team who held out longer. Next round, the losing team will start as the Survivors (the opposite of Versus, in which the losing team is Infected first). The game will end as soon as it is impossible for the losing team to win. For example: a game of 3 rounds ends as soon as a team wins 2 rounds.

The team that wins the most rounds wins the game. Because of this, scoring is not based on the total amount of gas cans collected over the entire game. In other words, a team can win even if, overall, they collected fewer gas cans than their opponents as long as they win more rounds.

During a game, overtime will occur if the time limit runs out, but at least one Survivor is holding a gas can. Overtime is indicated by the timer flashing red. During overtime, the Survivors have an indefinite amount of time to pour another gas can into the generator and extend the time, so long as at least one Survivor is holding a gas can at all times. If all the gas cans are dropped, the Survivors' round is over. Overtime can occur multiple times during a single round.

Gas cans and pouring
Gas cans have a white aura, so Survivors can see them anywhere on the map. If they are picked up and dropped they will have an orange aura. Gas cans always spawn in the same location on the map. If they get destroyed, they will eventually respawn back at the location they originated. The only Infected that can destroy gas cans with its attack is the Spitter. However, the attack only works if the gas can has been previously picked up and dropped. When gas cans are hit with acid they will flash orange momentary, then explode. While flashing, Survivors will have time to pick up the gas cans before they explode. It takes about 2.5 seconds to pour fuel into the generator. However, any damage from Infected will instantly restart the pour timer (friendly fire will not), so a Survivor must not be under attack in order to complete the process.

Maps and supplies
There are currently 18 official maps available for Scavenge Mode. The maps are mostly identical to their corresponding levels; however, they have been modified to block off certain areas to limit the gameplay area and provide more supplies for the Survivors, similar to Survival Mode. The area around the generator where Survivors spawn usually contains three Tier 2 weapons, pills, adrenaline shots, grenades, four first-aid kits, an ammo pile, and at least one melee weapon. Other supplies are scattered around the maps, usually near gas can spawns. The grenade launcher only spawns on certain maps. The amount, the location, and the types of supplies always stay the same on each map.

Infected

 * After set-up time ends, don't be too eager to spawn. The Survivors may go to an area nowhere near where you were planning to spawn.
 * In Scavenge Mode, it isn't just about incapacitating all of the Survivors. If the timer is low, preventing them from grabbing fuel with simple attacks can help end the Survivors' turn.
 * Try to focus your attacks on Survivors either carrying or pouring the gas cans. Any type of attack by an Infected will reset the pour timer for a Survivor. If a lone Survivor is pouring a gas can, pounce, pull, charge, or ride them. This will not only delay the pouring, but make them drop the can. This is particularly important in overtime, because the instant the gas cans are dropped, the Survivor's turn ends. The basic Special Infected claw or punch attack will also delay pouring (though it does not make the player drop the gas can).
 * Spitter acid will also delay a Survivor from fueling the generator (though it does not make the player drop the gas can). Make sure to spit a few seconds before they reach the generator. This is because it takes a short amount of time for the spit to travel and when the spit hits the ground, it takes a little bit more time to spread, before it does any damage.
 * If there's an opportunity, go for any Survivors that are by themselves and very far away from both the rest of the Survivors and the generator, whether or not they have a gas can. One of three beneficial things can happen: the team will stop fueling and help the Survivor; they'll ignore the Survivor and let them die; or a single Survivor will come to the rescue, giving an Infected partner the opportunity to grab another lone Survivor.
 * Many gas cans are enclosed and hard to reach or see from most spots. These are good areas to camp in case a lone Survivor comes by to grab a gas can.

Survivors

 * Don't try to pour fuel into the generator when you are being hit. Any damage will instantly restart the time it takes to empty a gas can, so it is best to kill any Infected attacking you first before you put the fuel in.
 * Always have at least one other Survivor near you at all times.
 * If you discover a Spitter is on the map, make sure to kill her quickly. She can destroy Gas cans and delay pouring fuel into the generator.
 * Use long-range weapons, such as the Combat Rifle or Sniper Rifle. There are not that many Common Infected on the maps and using a long-range weapon is better suited for killing Special Infected, especially if they can move Survivors far away from the group.
 * If you start the round as Survivors, go for the farthest gas cans first, while your team has very good health and supply slots are filled. However, if your team is not good and/or the Infected team is very good, go for the closest gas cans first.
 * If you have it, use your Adrenaline in a pinch as you can pour gas faster and you will still pour your gas in while getting hit. This is especially useful if the round is about to end.
 * If your team is badly injured and you have tied your opponents' gas can count, it may be strategically effective to commit suicide. The game uses the time taken to complete a round as the tiebreaker; if you die faster, your round takes less time and you are more likely to win. Only do this if you do not believe you can get another gas can before your team dies, or if you know you were faster than the other team.
 * Instead of running with a single can in hand, you can "juggle" gas cans. Throw one ahead of you, pick up another, throw it forward, move forward, pick up the first can, throw it forward etc. Done right, and you can juggle 4 or 5 cans at a speed only slightly less than a normal run (not actually juggling, the cans are expected to hit the ground and hopefully roll forward a bit).
 * It is significantly faster to collect multiple groups of cans at the same time instead of running back to the generator for each group of cans. Use juggling to grab as many cans as you can before heading back to save time.
 * Be careful when transporting large numbers of gas cans; if you leave any unattended even briefly, a Spitter may be able to spit on it, forcing you to go through the spit to save the can or let the can be destroyed.
 * On some maps, it is possible to throw gas cans very close to the generator even if you have to take a longer route to reach it (examples include throwing cans down from the third floor of the Atrium or throwing cans up to the generator from the lower level of the roof on Rooftop). Take advantage of this to get gas cans to the generator even faster. (However, if you leave them unattended, a Spitter can destroy them.)

Dead Center

 * Mall Atrium

The Passing

 * The Riverbank
 * The Underground
 * Port

Dark Carnival

 * Motel

Swamp Fever

 * Plank Country

Hard Rain

 * Milltown
 * Sugar Mill
 * Mill Escape

The Parish

 * Park

The Sacrifice

 * Brick Factory
 * Barge

No Mercy

 * The Apartments
 * Rooftop Finale

Crash Course

 * The Alleys

Death Toll

 * The Church

Dead Air

 * The Terminal

Blood Harvest

 * Farmhouse Finale