US-raised Gordon and Ohio-born Mullens, who play for the Detroit Pistons and the Charlotte Bobcats respectively, have yet to play for GB.
Chicago Bulls forward Deng, a GB regular, is also included in the squad.
Coach Chris Finch will reduce the group to 16 in May and then make a final cut to 12 at the start of July.
Finch said: "We have the potential for a world-class team who will surprise a few people this summer.
"The commitment from all our players to the programme once again is great and it's also good to see our strength and depth continuing to increase year on year."
Preliminary squad (including club and nation): Kieron Achara (Manresa (Spain)/Scotland), Ogo Adegboye (Apoel Nicosia (Cyprus)/England), Robert Archibald (Zaragoza (Spain)/Scotland), Eric Boateng (Peristeri (Greece)/ England), Matthew Bryan-Amaning (Hacettepe (Turkey)/England), Dan Clark (Estudiantes (Spain)/England), Luol Deng (Chicago Bulls (USA)/England), Joel Freeland (Malaga (Spain)/England), Ben Gordon (Detroit Pistons (USA)/England), Kyle Johnson (Apoel Nicosia (Cyprus)/England), Andrew Lawrence (College of Charleston (USA)/England), Mike Lenzly (Nymburk (Czech Republic)/England), Alex Marcotullio (Northwestern College/Scotland), Pops Mensah-Bonsu (Besiktas (Turkey)/England), Byron Mullens (Charlotte Bobcats (USA)/England), Sullivan Phillips (Prievidza (Slovakia)/England), Nate Reinking (Sheffield/England), Ryan Richards (unattached/England), Ovie Soko (University of Alabama (USA)/England), Andrew Sullivan (Leicester/England), Devon van Oostrum (Tarragona (Spain)/England).
Elsewhere there are few surprises in what is by some margin the strongest squad Great Britain have ever pulled together. Deng was voted an NBA All-Star this season and has again been a rock all season for the Chicago Bulls despite having to manage a tendon injury to his left, non-shooting hand.
The Sudanese-born Deng, first captained GB age group teams when his family moved to London and he has been playing regularly at senior level since 2007 contributing a huge amount to Great Britain's attempts to "justify" their participation in the Olympic tournament by twice qualifying for the Eurobasket finals.
When Gordon was at the Bulls the two worked particularly well together and Great Britain will be hoping they can reproduce that chemistry.
Pops Mensah Bonsu – another with NBA experience – has been back to his spectacular best playing in the strong Turkish League after missing much of last season through shoulder injury while Joel Freeland is bound to be another stalwart of the squad and has been enjoying another solid season for Unicaja Malaga in the ACB League in Spain, the second strongest in the world behind the NBA
Finch has once again shown his belief in the wealth of young players that have been working their way up through GB’s performance pathway. Having been blooded last year the likes of Kyle Johnson, Andrew Lawrence, Alex Marcotullio, Ryan Richards, and Devon van Oostrum will all be given a chance to bid for Olympic inclusion.
A couple of newish names are former GB U20 player Ovie Soko while Sullivan Phillips, who plays with Prievidza in Slovakia, is a new addition to the roster.
“The GB basketball programme has come a long way since 2006 and the blend we have now of experienced talent with the younger guys is fantastic to see. We have the potential for a world class team who will surprise a few people this summer. The commitment from all our players to the programme once again is great and it’s also good to see our strength and depth continuing to increase year on year."
Finch is right to accentuate the positive. On paper Great Britain should be able to put a starting five on court that at least bares comparison with most side bars USA and Spain – the big test at the Olympics though will be if the next tranche can step up.
To be truly competitive it is the strength of the bench that will be crucial and that is where Great Britain have much work do this summer.
The squad will be trimmed to 16 in May and will head to Houston, Texas for an intensive-three week camp in June that will include double headers against Russia and Lithuania before they embark on an extensive tour of Britain and Europe playing warm-up matches that will include a first ever match against the Dream Team.