(CNN) - A four-CD box set of previously unreleased material by Tom Petty and the Heartbreakers is set to be released in September, SiriusXM announced Tuesday.
"An American Treasure" is the first posthumous musical project since the rocker died of an accidental overdose in October. He was 66.
According to Rolling Stone, the collection will include 60 "previously unreleased studio recordings, live recordings, deep cuts and alternate versions of popular Petty songs."
SiriusXM debuted a portion of one of the songs, "Keep a Little Soul," on its Tom Petty channel Tuesday.
With hits like "American Girl," "Don't Do Me Like That" and "Learning to Fly," Petty and his longtime band were famed for an instantly recognizable brand of sturdy, heartland rock that made them a classic-radio staple for decades.
They were inducted into the Rock and Roll Hall of Fame in 2002.
"An American Treasure" is set to be released September 28.