Betfair has Romney at 0.7% and Ryan at 0.4%. Can't really see it being any higher than that, given that we already have plenty of candidates who are actually running for the nomination.
A more interesting question: How many of the 15 candidates currently in the race are less likely to win the nomination than Romney?
Does Jack Fellure count?
Jim Gilmore and George Pataki are more likely answers.
I don't know if it's just them. I think I'd probably rate Romney as more likely to be the nominee than Santorum, tbh. Though comparing the relative likelihood of <1% events isn't easy.
I'm reminded of 2008, when Tweed posted a poll about who is more likely to be the GOP nominee, George W. Bush or Jeb Bush? Jeb wasn't running, and George was constitutionally ineligible to run for a third term, but Tweed argued that George declaring martial law and ignoring the constitutional prohibition on a third term was more likely than Jeb somehow emerging from a brokered convention scenario, when he didn't run during the primaries.
