According to Access Hollywood:
The Academy of Motion Picture Arts and Sciences has ruled that only
Graham King will get the credit for the crime drama “The Departed,”
leaving Brad Pitt and Paramount Pictures studio chief Brad Grey out in
the cold.
[...]
When a film wins an Oscar, it’s the producer who accepts the golden
statuette and gives the acceptance speech. Rules adopted by the
academy in 2000 limits credited producers to three in order to avoid
handing awards to a mob of “producers,” some of whom may have gained
the credit for little or no effort.
[...]
The academy also decided that only one producer would get credit for
the Martin Scorsese film “The Departed.”