Self-styled King of Pop Michael Jackson is back from the grave again this week with a second posthumous album of songs recorded before his death in 2009.

"Xscape" went on sale in the United States on Tuesday, after being released in various European countries at the weekend and on Monday.

"This music has never been (previously) released," said L.A. Reid, the veteran American music mogul behind the project, on NBC television's "Today" breakfast program.

"Some of it has been leaked through the years.... but it wasn't widespread," said Reid, who sifted through a vault full of unreleased Jackson material to handpick the songs that appear on the album.

"I just listened to the songs that Michael sang completely from top to bottom, you know, multiple times," Reid said. "That was my guide -- and the ones that I thought had great melodies that would still stand up today."

Several critics have hailed "Xscape" as a clear improvement on 2010's "Michael," the first album released after Jackson died of a drug overdose at age 50, as part of a multi-record deal with Sony Music Entertainment.

"From the first, there was the voice .....Nearly five years after his death, that voice remains, and is at its most powerful on the new album," wrote the Los Angeles Times' reviewer.

The new album "feels shockingly vital, as though the producers charged with re-imagining this work had harnessed dance floor defibrillators," he wrote.

Ben Greenman of the New Yorker magazine called the album "a completely different beast from 'Michael'... Rather than rely on fragments or partial ideas, Reid focused on songs that were worked through by Michael from start to finish..."

Ironically, the songs on "Xscape" include one about child sex abuse, an issue that badly tarnished the King of Pop despite his acquittal of sexual molestation charges in 2005.

Jackson's executors have worked hard to pay off the enormous debts left by the fallen star, with key projects including the "This is It" film of rehearsals for the doomed world tour he was planning before he died in 2009.

"Michael" has sold a relatively modest 540,000 copies, according to Billboard magazine, which noted that Jackson's overall record sales were less than both Elvis Presley and Johnny Cash last year.

"Xscape" comprises eight songs chosen from the vast catalogue which Jackson worked on over four decades but which did not make it into any of his iconic albums like 1982's "Thriller" or 1987's "Bad."

The songs are based on original vocals by Jackson, who often made multiple recordings of tunes he was working on, but with music "contemporized" by a variety of producers for a modern audience.

While fans had to wait until this week to actually hear all the songs, the titles had been released in advance.

They included "Xscape," first produced 15 years ago, and "Do You Know Where Your Children Are." The latter is about "kids being raised in a broken family where the father comes home drunk and the mother is out prostituting and the kids run away from home and they become the victims," according to the liner notes.

US rapper Timbaland, executive producer on "Xscape," said they were keenly aware of the need for the new Jackson record to stand up against the best that current pop music has to offer.

"How would I hear this on the radio against Katy Perry? Would it sound old, would it sound new?" asked the producer, who works closely with Justin Timberlake and Beyonce.

He "had to make sure that it can compete with everything that is going on today in the pop world," Timbaland told Billboard.