There are six players who come into the squad after missing out on the Guinness Autumn series.
Celtic League champions Ulster contribute eight players, with Leinster's Gordon D'Arcy returning to an almost full-strength squad which is missing only the suspended Alan Quinlan and the injured Stephen Ferris.
"The championship is a long and hard tournament that that will always test your resources, so I felt that we needed to increase our squad to 35 to give us some extra cover," said O'Sullivan. "We have a good injury profile at the moment and with the return of players from injury, such as Tommy Bowe and Jerry Flannery as well as the other additions to the squad, it will push up the competition levels.
"While there are not many changes from November, the squad is always selected on form and this group reflects that. The Championship is our bread and butter tournament and is the one we always want to do well in. We were pleased with how the Guinness Autumn Series went but this tournament is a step up and we will have to raise our performances another level. An away trip to the Millennium stadium to play Wales is one of the toughest openings you could get at this moment in time and all we will be focusing on is trying to get the right performance against an excellent Welsh team".
Ireland Squad
Forwards (18):
Neil Best (Belfast Harlequins/Ulster)
Rory Best (Belfast Harlequins/Ulster)
Simon Best (Belfast Harlequins/Ulster)
Simon Easterby (Llaneli)
Jerry Flannery (Shannon/Munster)
Keith Gleeson (St.Mary's College/Leinster)
John Hayes (Bruff/Munster)
Jamie Heaslip (Clontarf/Leinster)
Trevor Hogan (Shannon/Leinster)
Marcus Horan (Shannon/Munster)
Denis Leamy (Cork Constitution/Munster)
Donncha O'Callaghan (Cork Constitution/Munster)
Paul O'Connell (Young Munster/Munster)
Mick O'Driscoll (Cork Constitution/Munster)
Malcolm O'Kelly (St.Mary's College/Leinster)
Frankie Sheahan (Cork Constitution/Munster)
David Wallace (Garryowen/Munster)
Bryan Young (Ballymena/Ulster)
Backs (17):
Isaac Boss (Ballymena/Ulster)
Tommy Bowe (Belfast Harlequins/Ulster)
Girvan Dempsey (Terenure College/Leinster)
Gordon D'Arcy (Lansdowne/Leinster)
Luke Fitzgerald (Blackrock College/Leinster)
Shane Horgan (Lansdowne/Leinster)
Denis Hickie (St.Mary's College/Leinster)
Robert Kearney (UCD/Leinster)
John Kelly (Cork Constitution/Munster)
Barry Murphy (U.L. Bohemians/Munster)
Geordan Murphy (Leicester Tigers)
Brian O'Driscoll (Blackrock College/Leinster)
Ronan O'Gara (Cork Constitution/Munster)
Eoin Reddan (Wasps)
Peter Stringer (Shannon/Munster)
Andrew Trimble (Ballymena/Ulster)
Paddy Wallace (Ballymena/Ulster)
Not considered due to injury:
Stephen Ferris (Dungannon/Ulster) {Hand}
Not considered due to suspension:
Alan Quinlan (Shannon/Munster)
