An exercise rider works out Kentucky Derby hopeful Justify at Churchill Downs in Louisville. USA Today Sports

The Kentucky Derby is just four days away, with no clear-cut favorite in a field that has over 20 horses. Six horses have better than 10-1 odds, but there is no contender with better than 4-1 odds.

The six horses to perhaps focus on are Justify (+425), Mendelssohn (+525), Bolt D’Oro (+625), Audible (+725), Magnum Moon (+805) and Good Magic (+850).

Audible has the No. 5 post for Saturday’s race, which was the same post as the 2017 winner Always Dreaming. Justify has the No. 7 post, while Mendelssohn has the No. 14 post. Good Magic is at No. 6 and Magnum Moon is at No. 16.

While the top contenders typically get considerable attention, many oddsmakers have liked the chances of some longshots. Firenze Fire is the biggest longshot at +8050.

"This year's Kentucky Derby will be challenging for oddsmakers as again there is no single clear-cut favorite," D.J. Fields, odds consultant for offshore sportsbook Bookmaker.eu. told International Business Times in an email.

There has already been tremendous movement in a wide-open field, according to Fields.

"No horse has commanded more wagering volume than Justify. In early March, he opened as a 14-1 shot, but he is now the favorite to win it all with the odds slightly north of 4-1.

"Mendelssohn has been drawing money as well, opening as 4-to01 favorite, however currently is listed at 5-to-1 behind Justify.

"With a wide-open field several dark horses have been causing quite a stir, but none so much as Magnum Moon. The undefeated Magnum Moon opened up as at 25.5-to-1, but bettors have driven that line down to 8-to-1. Surprisingly, except for Justified, we have written more action on Magnum Moon than any other horse in the Run for the Roses thus far.

"Our most significant liability will be Audible. In February he opened up as an 80-to-1 shot and players saw some real value in the eventual Florida Derby winner. Currently sitting at 7-to-1 we are facing some severe exposure if Audible can win the most exciting two minutes in sports."

The winning purse of the Kentucky Derby is $2 million with the winner receiving roughly $1.24 million.

Kentucky Derby Odds (Bookmaker.EU)

Justify +425

Mendelssohn +525

Bolt D’’Oro +625

Audible +725

Magnum Moon +805

Good Magic +850

Vino Rosso +1,350

Hofburg +1,415

My Boy Jack +2,350

Solomini +2,450

Noble Indy +3,050

Enticed +3,550

Flameaway +3,557

Free Drop Billy +3,550

Instilled Regard +4,550

Sporting Chance +4,550

Combatant +5,250

Bravazo +6,050

Lone Sailor +6,550

Promises Fulfilled +6,550

Firenze Fire +8,050

An exercise rider works out Kentucky Derby hopeful Justify at Churchill Downs in Louisville, Kentucky, U.S., May 1, 2018. Jamie Rhodes-USA TODAY Sports