Right now at Primary.guide, you can read the current betting market odds for a “contested convention” and a “brokered convention.”  The definitions are as follows.  A contested convention means that no candidate has 1237 delegates by the end of the last primary.  A brokered convention means that no candidate wins on the first ballot at the convention.

Right now the odds of a brokered convention are 50%.  Note also that the odds of a Trump nomination are 50% as well.  And Trump is the only candidate with any chance of winning a majority on the first ballot (even if he doesn’t get 1237 bound delegates he will be close and no other candidate could combine their bound delegates with unbound delegates to get to a majority.)

Thus, if there is no brokered convention Trump is the nominee.  The probability of no brokered convention is 50%.  Thus the entire 50% probability of a Trump nomination is accounted for by the event that he wins on the first ballot.

In other words there is zero probability, according to betting markets, that Trump wins a brokered convention.

The odds of a contested convention are 80%. That means that betting markets think there is a 30% chance Trump fails to get 1237 bound delegates but still wins on the first round.  I.e. according to betting markets we have the following three mutually exclusive events:

1. Trump gets to 1237 by June 7.  20% odds
2. Trump fails to get 1237 bound delegates but wins on the first ballot.  30%
3. Nobody wins on the first ballot and Trump is not the nominee.  50%