"The team to face England at Twickenham will be selected from this training squad," said Gatland.
"We have established a nucleus of players who will form our World Cup squad based on their performances in training over recent weeks but it is now time to translate those efforts on to the field.
"The players have worked hard but places in that final World Cup squad are still very much up for grabs and a lot will depend on what we see over these next three games.
"We have not shied away from facing the top quality opposition in preparation for this World Cup and it doesn't come much tougher than facing the 2003 World Cup winners and 2007 finalists on their home patch."
Wales face England at Twickenham on Sunday before playing the English again at the Millennium Stadium seven days later.
Argentina provide the final opposition on home soil on August 21 before a 30-man Wales squad for the World Cup is named two days later.
Wales squad
Scott Andrews, Gethin Jenkins (Blues), Lloyd Burns (Dragons), Huw Bennett, Ryan Bevington, Adam Jones, Paul James (Ospreys), Ken Owens, Matthew Rees (Scarlets), Craig Mitchell (Exeter Chiefs), Bradley Davies, Sam Warburton, Martyn Williams (Blues), Luke Charteris, Danny Lydiate, Toby Faletau (Dragons), Ryan Jones, Alun Wyn Jones, Jonathan Thomas, Justin Tipuric (Ospreys), Josh Turnbull, (Scarlets), Gareth Delve (Melbourne Rebels), Andy Powell (Sale Sharks), Michael Phillips (Bayonne), Lloyd Williams (Blues), Tavis Knoyle (Scarlets), Jamie Roberts (Blues), James Hook (Perpignan) Jonathan Davies, Stephen Jones, Rhys Priestland, Scott Williams (Scarlets), Gavin Henson (unattached), Leigh Halfpenny (Blues), Lee Byrne (Clermont Auvergne), Aled Brew (Dragons), Shane Williams (Ospreys), George North, Morgan Stoddart (Scarlets).