O'Neill's men play Oman in a friendly on September 3, four days before their opening Euro 2016 qualifier in Georgia, with the first game giving him a final chance to assess his options.
There are no uncapped players in the party, but O'Neill will be without veteran defender Richard Dunne, who announced his retirement from international football during the summer.
The squad includes former first-choice goalkeeper Keiren Westwood, who has returned to club action after joining Sheffield Wednesday following his release by Sunderland at the end of the last campaign.
O'Neill also confirmed that Los Angeles Galaxy striker Robbie Keane will remain his captain.
The Republic failed to qualify for last summer's World Cup finals and they have another tough task in Group D of the European qualifiers against world champions Germany along with Scotland, Poland, Georgia and Gibraltar.
They made it to the finals of the last European Championship in Poland and Ukraine in 2012, but lost all three group games as they embarked upon a downward spiral which ultimately cost then manager Giovanni Trapattoni his job.
O'Neill, assisted by Roy Keane, took over in November last year and his seven friendly matches to date have brought one win, three draws and three defeats.
He said: "I have had the opportunity to work with the players since last November, and we are well prepared as we embark upon the first of our qualifiers next month.
"Oman will provide a good test to start our trip before we travel to Tbilisi. We are focused on the task in hand, and look forward to the challenges ahead of us."
Republic of Ireland squad: Forde (Millwall), Westwood, (Sheffield Wednesday), Randolph (Birmingham), Elliot (Sunderland), Keogh (Derby), Wilson (Stoke), Coleman (Everton), O'Shea (Sunderland), Pearce (Reading), Kelly (Reading), McShane (Hull), Delaney (Crystal Palace), O'Brien (West Ham), Duffy (Everton), McCarthy (Everton), Hendrick (Derby), Clark (Aston Villa), Ward (Burnley), Whelan (Stoke), Gibson (Everton), Reid (Nottingham Forest), McGeady (Everton), Pilkington (Cardiff), McClean (Wigan), Brady (Hull), Quinn (Hull), Meyler (Hull), Hoolahan (Norwich), Keane (LA Galaxy), Long (Southampton), Murphy (Ipswich), Walters (Stoke), Doyle (Wolves), Stokes (Celtic), Cox (Reading), Sammon (Ipswich).