On PredictIt.com, operated by Victoria University in Wellington, New Zealand, the predicted chances of the Texas senator winning the nomination for the Nov. 8 election rose to 10 percent as results from Super Tuesday voting continued to be tallied.
Cruz has gained 4 percentage points in the past two days and his predicted chances stood at the highest level on the site since he tumbled to a record low after a weak showing in the South Carolina primary on Feb 20.
But Trump, who rolled to wins in at least seven states on Super Tuesday, was outdistancing both Cruz and his other top rival, U.S. Senator Marco Rubio of Florida. PredictIt had Trump's odds of winning the nomination at 76 percent early on Wednesday, down 4 points from Monday's record high of 80 percent.
Rubio, who scored his first win in a nominating contest on Tuesday with the Minnesota Republican caucuses, dropped 1 point to 10 percent, a record low for him.
Betting volumes on both Trump and Cruz hit records for the candidates on Tuesday and Rubio's volume was his second highest ever.
Other online betting venues also gave Trump, a New York billionaire businessman, the strongest odds of winning the nomination. Ireland's PaddyPower put Trump as a 1-to-7 favorite, with Rubio following at 5-1 and Cruz at 12-1.
Ladbrokes PLC said on Wednesday morning that Trump's odds of securing the nomination were 1-5. Rubio came in a distant second at 9-2, followed by Cruz at 25-1.
Message boards associated with PredictIt featured growing discussion of a possible brokered convention, which can occur when no candidate has won a clear majority of delegates before the start of the party's nominating convention.
There has not been a brokered U.S. major-party convention since 1952 when the Democrats nominated Illinois Governor Adlai Stevenson on the third ballot.
"I am betting against Trump getting the nomination at these odds but only because I think there is a 30 percent chance the GOP elite somehow successfully blocks him at the convention," said a post from a forum member with the username matthewcooley.