Sources told The Hollywood Reporter that the amount would be "substantial."
According to the site's information, the donation will be a lump sum – i.e., not a share of the movie's total profits, as some had suggested.
Immediately after the shooting, Warner and other studios said they would hold off announcing box-office figures out of consideration for the victims.
Anonymous sources, however, leaked early results to the press, and as soon as Sunday morning The Dark Knight Rises was widely reported to have enjoyed one of the most successful opening weekends in history – coverage which some critics found distasteful.
"The movie's going to gross over a billion dollars worldwide by the time it leaves theaters," wrote an angry Connor Simpson on The Atlantic Wire. "You can spare $20 million, Warner."
The studio looks set to face at least one lawsuit as a result of the shooting: a lawyer for one of the survivors told TMZ that his client planned to sue Warner Bros. for making a violent movie that – the lawyer claims – the gunman partly mimicked. Torrence Brown, Jr., who was uninjured in the attack, also plans to sue the Century 16 movie theater and the suspect's doctors, attorney Donald Karpel said.
Anticipating similar criticism, Warner has already made changes to its next blockbuster: Variety quotes a source as saying that the studio decided to cut an eerily prescient scene from Gangster Squad, due out in September, in which gunmen open fire on a movie-theater audience.