It’s been nearly 16 years since Oasis’ Liam and Noel Gallagher last performed on stage together.

This Friday in Cardiff, Wales, the feuding siblings will come together to kick off a worldwide tour expected to bring in upwards of $200 million, as estimated by industry professionals.

Their agreement with concert promoter Live Nation is valued at $170 million, and they’ve also secured a $27 million deal for merchandising rights to their likenesses, along with a lucrative partnership with Adidas.

The group—known for ’90s anthems like “Wonderwall” and “Champagne Supernova”—is reportedly discussing a documentary collaboration with Netflix to coincide with the tour, according to sources from The Post.

“Let’s not kid ourselves, it’s all about the money,” said one noted British music rep who has worked with many iconic bands. “And the money is ginormous.

“If it wasn’t just about the cash they would have made some new music like The Rolling Stones last year with ‘Hackney Diamonds,’ which went to No. 1 [in the UK and No. 3 in the US],” the rep added.

(The band announced Wednesday they are re-releasing a 30th-anniversary edition of the album “(What’s The Story) Morning Glory?” on October 3, with new unplugged versions of their hits.)

It all comes after decades of Liam, 52, and Noel, 58, not speaking to each other.

And even though they will be traveling on a private jet with the band’s name splashed on the side, don’t expect too much brotherly love.

The Gallaghers still have separate representation — and plenty of tour insurance in case things fall apart and they refuse to play together, just like in the old days.

“Liam could be pretty unpleasant when he was off his head with booze, he’s a bit of a yob,” said the rep. “Noel is very pleasant and intelligent … having met them both, you can see they are chalk and cheese.”

Liam – who is about to become a grandfather, as his daughter Molly Moorish-Gallagher is pregnant — has said he stopped drinking before performing, in part because of a famously disastrous 2000 concert at Wembley Stadium when he messed up the lyrics, talked about his divorce and asked to see female fans’ breasts on the Jumbotron.

Asked if the band will actually make it through the 41-date tour, including sold-out stadium shows in Chicago, Los Angeles and New Jersey, as well as through Asia, Australia and South America, the rep said: “With that money they will make it! They’ll easily get through the UK shows, and there will undoubtedly be millions in insurance if they don’t.”

“I think they’re motivated to put on a good show for the fans,” said a source familiar with the Live Nation deal, which, The Post is told, took around a year to finalize. “They’ve been rehearsing for the past month.”

Oasis will get around $6.8 million per show, the source revealed, adding, “The reality is that there is an ongoing conversation about what a home entertainment deal looks like [to live-stream tour dates] and they are in talks with a streaming partner for a documentary.

“I know they turned down Netflix because they wanted to produce the film themselves.”

The brothers’ rivalry began with Liam’s birth, according to their mom, Peggy.

“Noel was absolutely beautiful as a baby and then of course Liam comes along and it takes the limelight off him,” she once reminisced.

Liam founded Oasis when Noel was a roadie with another Manchester band, Inspiral Carpets, and convinced his big brother to join.

Noel became their chief songwriter, responsible for mega-hits like “Don’t Look Back in Anger.”

But the siblings became as well known for their antics and insults as their music.

They made a crazed LA debut at the Whiskey A Go Go on the Sunset Strip in 1994 after some band members accidentally took crystal meth.

“I don’t know who f–king got it but it was there and we all thought it was coke,” Liam says in the 2016 “Oasis: Supersonic” documentary. “We’re doing big f–king lines of it and it just kept us up for f–king days. The band were not in the right place.”

The set ended with Liam shouting insults at the audience and bopping Noel with a tambourine — and Noel storming off and quitting the band for two weeks. 

“I did travel to LA to photograph them in ’94 at the Whiskey on Sunset. But let’s say it wasn’t their finest moment,” photographer Kevin Cummins told The Post. “It almost split the band up before they’d started to gather momentum.”

“For showbiz journalists in the late 1990s, Oasis were a godsend,” said Nicole Lampert, former deputy editor of The Sun’s Bizarre showbiz column. “They were always up to no good and they were always starting fights.”

As their fame grew, so did the brothers’ legendary fallouts.

When Liam invited a group of strangers he’d just met at a local pub to watch Noel recording in studio in 1995, Noel smashed Liam over the head with a cricket bat.

The bat later sold at auction, for an undisclosed price, with a certificate of authenticity.

Liam left Noel to perform his vocals during the recording of an “MTV Unplugged” session at London’s Royal Festival Hall in 1996, claiming to have laryngitis. But he then showed up in the hall’s balcony, smoking, drinking and heckling his brother. When he eventually tried to jump onstage, Noel told him to “piss off.”

Noel later called Liam “the angriest man you’ll ever meet,” telling Q magazine, “He’s like a man with a fork in a world of soup.”

The band’s last gig took place on August 22, 2009, at the UK’s V Festival.

By that point Noel and Liam had reached a simmering point where they only saw each other on stage and didn’t even travel together.

Things came to a head days later when they were due to play Paris’ Rock en Seine festival, but Noel didn’t even make it through the curtains following a pre-show brawl.

Liam had smashed one of his prized guitars and Noel walked out, announcing he was leaving with “some sadness and great relief.”

Promoting his solo album two years later, Noel said the fight had spiraled after a squabble about Liam’s demands for a free plug for his clothing range in the tour program — and said his brother had become  “quite violent.”

After cursing out everyone, Noel said, “he picked up a plum and threw it across the dressing room and it smashed against the wall. Part of me wishes it did end like that, that would have been a great headline: ‘Plum throws plum and finishes f–king Oasis.’

“He went to his dressing room and he came back with a guitar and he started wielding it like an axe — he nearly took my face off.”

For his part, Liam has said: “Noel was acting like a d–k, I was acting like a d–k. Two d–kheads in a room — f–king hell. Band over.”

Cummins, who recently published the book “Oasis: The Masterplan,” added, “I think it’s great that they’re back together for the gigs. The fact that half the UK tried to buy tickets shows how much love there is for the band. People are traveling from all over the world to go to gigs on other continents too — they’re a global phenomenon.”

And Liam recently announced that his life is very different now. “After party’s are for wankers[.] I’m getting straight off after the gigs[,] get my beauty sleep[.] This level of sexiness doesn’t happen by staying up talking bollox to bellends.”