The Competition and Consumer Protection Commission has opened an investigation into Ticketmaster and its handling of Oasis tickets.
The use of so-called dynamic pricing saw tickets rise to over 415 euro for standard standing tickets.
The consumer watchdog got over 100 complaints about the experience of buying Oasis tickets for Croke Park.
The CCPC says while companies are allowed to respond to demand - there are what are described as 'legitimate concerns' over how people were treated.
It has now opened an investigation to see if consumer protection laws were broken.
The watchdog is also accepting more complaints about the experience of buying tickets.
Oasis are playing two shows at Dublin's Croke Park next August, and announced a comeback - 15 years on from breaking up.
In a statement, the CCPC said, "the CCPC has reviewed more than 100 contacts from consumers who are very disappointed and frustrated about their experience of buying tickets for Oasis concerts.
"While companies in Ireland are allowed to respond to market demand, there are legitimate concerns over how consumers were treated and we have decided that an in-depth investigation is necessary.
"If we find that consumer protection laws were broken we will take action.
"The CCPC is grateful to consumers who have taken the time to call or email our helpline to share their experiences with us as their stories have helped us develop a picture of last weekend’s events."
