The Ballydoyle handler equalled Bobby Frankel's record with Hydrangea at Ascot on Saturday and is responsible for more than half of the entries in the mile contest.
Spearheading O'Brien's potential team are leading Investec Derby fancies Saxon Warrior and The Pentagon.
Mendelssohn, Seahenge and Threeandfourpence, who finished second, third and fourth respectively in the Dewhurst, have also been left in, along with Zetland Stakes winner Kew Gardens and Royal Lodge runner-up Nelson.
Coat Of Arms, Delano Roosevelt, Hunting Horn, Lucius Tiberius and Saracen Knight complete his list of contenders.
National Stakes winner Verbal Dexterity missed the Dewhurst due to a bad scope, but he is one of two potential runners along with Theobald for trainer Jim Bolger, who is bidding for a first winner in the race.
Bolger told At The Races: "He scoped clean last Thursday. He was in very good form all along so we were able to keep him exercised.
"He did a bit of work on Saturday morning, I was very happy with that. He'll work again on Tuesday and that should leave him ready for the Racing Post Trophy. That's the objective at the moment.
"I wouldn't be looking back (at the Dewhurst). Hopefully we get the business done in Doncaster."
John Gosden's Royal Lodge winner Roaring Lion heads the home-trained team while Charlie Appleby could be double-handed with Solario Stakes hero Masar and first-time-out Goodwood winner Loxley, who was the sole supplementary entry.
The list is completed by Alfa McGuire (Bryan Smart), Chilean (Martyn Meade), Hey Gaman (James Tate), Gabr (Sir Michael Stoute) and Merlin Magic (David Elsworth).
Sky Bet odds: 9/4 Saxon Warrior; 3/1 The Pentagon; 4/1 Verbal Dexterity; 5/1 Roaring Lion; 7/1 Masar; 9/1 Chilean; 12/1 bar
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