During the Supreme Court's Health Care deliberations, the Intrade market overwhelmingly thought the court would strike down the law's centerpiece, the individual mandate requiring most Americans to buy health insurance. In the week before the court's ruling, betters gave the mandate a 76 percent chance of being ruled unconstitutional.
But the betters were wrong. The court upheld the mandate in a close 5-4 ruling.
During the past presidential election, Intrade betters were way off on their Republican vice presidential pick as well. The day before GOP nominee John McCain named Alaska Gov. Sarah Palin as his running mate, Palin was trading at 1 percent on Intrade.
Intrade spokesman Carl Wolfenden said betting on running mates was not nearly as popular in 2008 as it has been in 2012.
"A lot of the reason why the vice presidential market is so popular this time around is there is kind of nothing else going on at the moment," Wolfenden said. "Last time we had two nominating battles that kept people busy, especially the Democratic one which went down to the wire."
But while betting markets like Intrade and BetFair have been pretty accurate in predicting election outcomes, Mike Smithson, a former BBC journalist and founder of PoliticalBetting.com said he does not think they are "in any way predictive" of whom Romney will choose as a running mate.
"This is down to the judgment of one man," Smithson said. "Where people themselves are involved in elections then you get a much greater say but where it's down to one individual decision, who knows how Mitt Romney's mind works."