The Fort Worth Star-Telegram said Buck's family paid a small finder's fee to an anonymous buyer for "The Eternal Wonder," a novel the writer apparently finished shortly before she died of cancer in 1973.
Her family and publishers said they were unaware of the book until the buyer of the storage-unit contents came forward, the newspaper said, adding it remains unclear how the literary treasure ended up in the storage unit.
A coming-of-age tale about a young man on patrol in the Korean Demilitarized Zone who finds romance in his travels, Buck's final book is to be published in October, more than 80 years after Buck's classic novel "The Good Earth" hit bookshelves, the Star-Telegram said.
"It's a novel that encompasses some of Buck's common themes: intercultural relationships, travel, China, Asia in general," Michael Carlisle, a partner at InkWell Management and a literary agent who represents the Buck estate, told the newspaper.
"This is a very, very exciting moment for anybody who loves the oeuvre of Pearl Buck."
"It is truly incredible to have a new novel by one of only two American women to win both the Nobel and Pulitzer prizes," publisher Tina Pohlman said.
Toni Morrison is the other writer to do so.