The Black Tar was a mind-control substance used by the Reapers that was pumped into water supply lines and water towers. The Black Tar was produced by Sasha, and was one of the powers granted to her by the Ray Sphere.
The Black Tar was transported via trucks, which were part of the side missions called "Mobile Poison". There were two other missions in which Cole had to stop the tar from spreading.
One was in the story mission "Nemesis Revealed", in which Cole had to destroy machines that pumped the tar into the water towers.
In the side mission "Dark Water", Cole had to do the same thing, but only once. It was revealed in one of John White's Dead drop that Sasha was experimenting on a form of the tar when she worked in the First Sons, possibly indicating she had powers before The Blast, or at least, was aware of them.
The Reapers applied the tar to citizens by kidnapping them and locking them in cages located in their hideout within the Jackson Tunnel. The Reapers then used a machine to coat the innocent civilians in the Black Tar until Sasha's mind-control kicked in and were given the Reaper uniforms and weapons. Sasha also had a machine that sucked the Black Tar from her and transferred it to the machine that sprayed it on the civilians.
The tar could also be turned into a gas as shown when Kessler and the First Sons kidnapped Sasha and drained the tar from her. The pedestrians would throw rocks, head butt and do anything they could to hurt Cole. He managed to take down the balloons delivering the gas to the citizens, thus preventing the First Sons from turning the entire city against him.
Near the end of the game, there was a news broadcast stating that a cure has been found for the tar. The reporter also stated that because of this, the lockdown would end in a couple of weeks. Although, if Cole was evil, he would not hear this broadcast.
Side effects of Black Tar immersion include hallucinations, sickness and a mental link with Sasha. Prolonged exposure can lead to death or mental control. Reapers will often throw up a black substance when fighting, likely the tar. This may mean that it multiplies within their bodies after prolonged exposure, or that continuous doses must be given to ensure continued mind control. Cole shows more resistance to the tar than anyone else, most likely due to his abilities.
- When you overload the tar kegs in the side missions of "Dark Water", you can create certain areas full of infected people.
- The Voice of Survival makes a reference to your actions on destroying the tar pumpers, claiming you are destroying the water supply.
- Black Tar is likely a reference to another game produced by Sucker Punch, Sly 3: Honor Among Thieves. In the first location of the game, Venice, the boss infects several water supplies with black tar, even though it is not as fatal.