Thousands of Oasis tickets listed on unauthorised sites will start to be cancelled "in the coming weeks", promoters have warned.
There was huge demand when they went on sale and many fans were angry at being stuck in online queues for hours only to miss out or find prices had rocketed.
People trying to sell their tickets for a profit are breaking the terms and conditions of sale.
Tickets will be cancelled by Ticketmaster or See Tickets and made available again at face value - with details to be announced shortly.
A spokesperson for the promoters said only 4% of tickets had found their way onto resale sites, which still amounts to tens of thousands.
"The examination of ticket sales is ongoing and the results will be passed to relevant law enforcement once complete where appropriate," a statement added.
Fans have been warned not to buy from authorised sites as their ticket could end up cancelled, while others could be fraudulent listings.
"If fans do want to sell Oasis tickets they can do so at face value through Ticketmaster or the band's official resale partner Twickets," the spokesperson added.
"For fans who believe they have had tickets cancelled in error, refer to the email sent by the relevant agent when informed."
Oasis begin their reunion on 4 July in Cardiff before playing another 16 dates in the UK and Ireland.
The tour then moves to Canada, the US, Mexico, and Australia.
It will be the first time the band have toured since the Gallagher brothers had an infamous falling out in 2009.
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The repercussions from the ticket-buying process have led to a proposed new law to improve pricing transparency and prevent fans from being ripped off.
The UK competition watchdog is also looking at the dynamic pricing system, which sees prices change according to demand.
Some tickets more than doubled from £148 to £355 when the Oasis UK shows went on sale as hundreds of thousands piled on to official websites.
Ticketmaster tried to fend off criticism by saying it did not set the pricing system, but fans' anger only grew when some tickets turned up on secondary sites at massively inflated prices.