Last year 177,000 people attended the Glastonbury Festival
Glastonbury organiser Michael Eavis says slow ticket sales in 2008 are due to terrible weather in previous years, not the choice of main headliner Jay-Z.
It is the first time in recent memory that tickets have not sold out on the first day.
100,000 had sold by Sunday afternoon out of a total of 137,500.
Michael Eavis said: "I think three years of mud may have taken their toll, but even so, 100,000 isn't bad."
The Verve and Kings of Leon are also headlining the festival this summer, which takes place at Worthy Farm from 27-29 June.
It has become common for most major UK festivals to sell out within hours.
Slow Sunday sales
Organiser Michael Eavis said: "It's a nice little sale for a Sunday morning. And that's without them even knowing who's playing - we haven't announced our line-up yet."
Kings of Leon headline the Pyramid Stage on Friday 27 June, with Jay-Z performing on Saturday 28 June and The Verve closing the festival on 29 June.
Hot Chip will top the bill on the Other Stage.
Other acts confirmed to play include British Sea Power, The Futureheads and music legends Leonard Cohen and Neil Diamond.
The full line-up will be announced on 1 May.
Michael Eavis added: "People will be astonished, astounded when they see who's playing.
"I'm so excited about Jay-Z too. He's the best thing we have had here for years."
Emily Eavis thinks a lot of people are choosing to go to European festivals this year as well.
She said: "I think the more festivals, the merrier. It might slightly affect the speed in which we sell tickets but ultimately I don't think it's anything really serious to worry about."
Organiser Michael Eavis is also denying newspaper reports that Jay-Z is about to pull out of headlining Glastonbury.
He said: "I don't know where that story comes from. It's absolute rubbish.
"We spoke to their people yesterday and they're absolutely all full of it.
"We're extremely proud to have him play here, I have to say that."