James Corden thinks doing 'Carpool Karaoke' with Sir Elton John was worth "hundreds of thousands of dollars".

Asked what viewers can expect from Elton, whose appearance airs during the show's Super Bowl special, James said: "We did 'Crocodile Rock,' and it's flamboyant.

"To sing 'Tiny Dancer' with Elton John in a car, you just think: If this was an auction prize, it would go for hundreds of thousands of dollars. I feel lucky every time I get in the car with any of these people who I just really admire and respect."

And James thinks his carpool guests - who have included Justin Bieber, Mariah Carey, Adele, One Direction and Coldplay's Chris Martin - have an equally nice time belting out their back catalogues.

Discussing Chris' recent appearance, he told Entertainment Weekly magazine:

"After every song he was like, 'Oh, I haven't heard that for ages!' Or, 'It brings me back to where I wrote this!.

"It's actually quite a lovely thing for them to reminisce; they hear their whole career in eight songs."

The British star thinks the segment shows a very different side to his guests.

He said: "There's an ease and an intimacy to it where you'd never ever see stars quite so unguarded.

"l'm different from when I'm doing the show when there's an audience of 200. Seeing a huge megastar sing their hits in the same environment that you and I sing on our way to work -- it's humanising."