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Nothing of the oil tanks history before the outbreak is known.
Post-Apocalypse[]
Following the start of the outbreak, the area was abandoned by any surviving inhabitants and left deserted. Eventually, a group of survivors set up camp by the giant oil tanks, but according to Melvin, they ignored the Vultures' warnings of the danger of such an action. The tanks bleeder valve got jammed on one of them, leading to an explosion that killed all of the survivors. The Vultures then swooped in and collected all of the survivors supplies before trapping all of the walkers in the area in the tanks with signs depicting how many walkers are inside.
AS Madison's group visits the nearby town in search of Charlie's family, splitting up and finding the town stripped of supplies as well as the remnants of the camp at the oil tanks. As Madison searches the camp, she is confronted by June who puts a gun to Madison's head and demands her keys. Madison quietly clicks her walkie button three times, signaling Strand and Luciana that she is in trouble. Madison, still at gunpoint, invites June to join her community. June instead snatches Madison's keys and starts to leave, before Alicia, Strand and Luciana cut her off. June runs to the top of an oil tank and falls through the roof. Madison jumps in after her and helps June fight walkers in a pool of oil. Alicia and Strand pry open the hatch to the tank and kill the remaining walkers and Alicia rescues Madison from a walker.
Later, at night, Luciana finds a copy of The Little Prince in the camp. Naomi insists that she's not from the area and doesn't know who led the walker into the tank. After hearing more walkers snarling, they decide to leave.
After the Vultures arrive at the Dell Diamond Baseball Stadium, Madison accuses Melvin of being responsible for the destruction of the camp. However, Melvin states that the survivors had ignored the Vultures' warnings about the dangers of the positioning of their camp and that "we had to clean up their mess."
Ennis loads the walkers from the oil tanks onto a truck and leaves with them.
Later, having been warned of Ennis' plan by Mel, Strand, holding a flag reading 457 reports to Madison Clark that the oil tanks were empty and all of the dead were gone. Charlie is unsure if Ennis will use them to attack the Dell Diamond Baseball Stadium while Strand and Cole reveal that the tanks run the whole length of the railway and they all once had walkers in them. The two men reveal flags showing that each tank held hundreds of walkers in them each before Ennis emptied them out, giving him a significant army.
The flags that Victor Strand and Cole recovered from the tanks are labeled 457, 583, 233, 619, 378 and 765. This means that 3,035 walkers were imprisoned in the tanks total.
