Las Vegas Sports Consultants made Duke a 7-5 favorite to win the title and a 2.5-point favorite to beat West Virginia in the semifinals on Saturday night, oddsmaker Kenny White said.
White said either Duke or West Virginia would likely be favored over Butler or Michigan State in the finals.
The Las Vegas-based firm that recommends betting lines to 90 percent of sports books in Nevada said Butler had a 5-2 chance of winning the title and put West Virginia's chances at 2-1 and Michigan State's at 17-5.
The firm said Butler is favored by 1.5 points in its game against Michigan State.
Michigan State (28-8) has reached the Final Four six of the past 12 years, but was expected to be an underdog with the Bulldogs playing near their home court in Indianapolis. Butler is listed as the host school for the Final Four.
"[The Spartans] were there last year -- that's quite an advantage -- but they are matched up on the road basically playing in Indianapolis," White said. "They'll be the underdog in both games."
The Las Vegas Hilton, which listed Duke as a 6-5 favorite and Michigan State as an 11-2 underdog, saw bettors flocking to Butler at 7-2 odds to win the title, said Chris Graham, race and sports coordinator.
"Butler's definitely the Cinderella," Graham said.
White said that despite the odds, the Final Four teams were not very far apart, with the widest spread for the finals expected at 4.5 or 5 points if Duke plays Michigan State.
"Anything could happen here, believe me," White said.