O'Brien and his father Aidan became the first father-son combination to win the Classic in 2012 with Camelot, and Guineas third Australia heads a four-strong team from Ballydoyle on Saturday afternoon.
Paddy Power had eased Australia to a best-priced 5-4 but O'Brien Jr said: "I'm really looking forward to it. Ever since he came into the yard and started working he's always been a good horse. He's bred to stay the trip, bred to handle the track and bred to win the Derby which is what you need going to Epsom. It's the ultimate test of a racehorse.
"You need to have a horse with pace, balance and that will get the trip. It's a funny track to ride at times, with Tattenham Corner and all the different things running down into the straight, it's the ultimate test of horse and rider. It's the race every jockey wants to win. He's got plenty of pace, hopefully he'll get the trip but it's an unknown, his mum and dad handled the track well. We're looking forward to it."
The bookmaker reported a couple of weeks ago that "a racing insider told our representative at Sandown that Geoffrey Chaucer absolutely smashed Australia in a Ballydoyle gallop"; the firm are not repenting.
Paddy Power said: "Pundits have yawned and called us 'the grandmasters of PR flim-flam' about our statement on the possible merits of Australia and Geoffrey Chaucer. But we're happy to put our money where our mouth is and take on the 'jolly', especially when Aidan is employing the scattergun approach."
Oisin Murphy will have his first Derby ride as Ed Dunlop has booked the apprentice of the moment for Red Galileo. He will warm up for that mount aboard the William Knight-trained course specialist Beacon Lady in the Investec Coronation Cup.
Red Galileo had some promising two-year-old form but has been fairly well beaten in the Sandown Classic Trial and Lingfield Derby Trial.
"We had a list of possible jockeys and after watching him win the Temple Stakes, the decision was made to book Oisin," said Dunlop. "My horses were ill earlier in the year, but this horse was supplemented and [the owner] is very keen to run."
Kevin Manning has been confirmed for the ride aboard Godolphin runner Sudden Wonder. The Charlie Appleby-trained colt finished third in the Lingfield Derby Trial and is one of three possible runners for Godolphin along with Appleby's Pinzolo and Saeed bin Suroor's True Story.
Appleby said: "I am very happy with Sudden Wonder's preparation to date and confident he will put up a big performance in the Investec Derby. I have spoken to connections and we agreed we would like Kevin Manning to be on board as his style of riding will suit Sudden Wonder. He is a very positive rider and experienced around Epsom. He partnered New Approach, Sudden Wonder's sire, to victory in the Derby."
Appleby has yet to make a decision about his other entry and said: "Pinzolo is suited by a sound surface so we will keep an eye on the weather, while Sudden Wonder has won on that type of going and soft ground."
William Buick, meanwhile, confirmed he has chosen Sandown Classic Trial winner Western Hymn over the fellow John Gosden-trained runner Romsdal.