By Stephen Mulvey
Internet betting websites and prediction markets are registering huge interest in the US presidential election, with trade already far exceeding the total for 2004 in some cases.
"Our volume is 600% up this presidential cycle, 2008 to date, versus 2004," said John Delaney, chief executive of Dublin-based political futures market Intrade.
Joe Biden is the bookies' favourite to be picked as Obama's running mate
The "gargantuan" struggle between Barack Obama and Hillary Clinton for the Democratic nomination had helped to fuel interest, he said, and now the sharp contrast between Mr Obama and John McCain was having the same effect.
"Two more diverse candidates you could not get," he said.
Intrade, which expects 2008 to outstrip 2004 by a factor of 10 by November, cashes in on the business of US users, who are forbidden from using sports betting websites.
But Irish bookmaker Paddy Power has also turned over more than three times more than it did in the whole of 2004 on the US presidential market.
Britain's Betfair has seen trade of £12m ($22.5m) on the US presidential race - less than the total for 2004, but enough to indicate that overall trade will be twice as much as four years ago.
According to Intrade the vice-presidential stakes - or veepstakes - are currently "stealing the limelight", with Barack Obama expected to make his choice very soon.
Democratic VP candidates Joe Biden and Evan Bayh are featured prominently on the Intrade website's front page, just above Republican frontrunners Mitt Romney and Tim Pawlenty.
The company said the VP market had been "frenzied" on Tuesday, with Joe Biden rising 18.9 points to close at 49.8 - indicating a roughly 50-50 expectation that he would end up as Barack Obama's running mate.
The Democratic veepstakes have been particularly volatile.
Joe Biden and his fellow frontrunners Evan Bayh and Tim Kaine were at long odds only a couple of months ago, and General Wesley Clark has made an impressive late surge.
Jim Webb, an early frontrunner, has all but disappeared from the frame, while other strong contenders Hillary Clinton and Kathleen Sebelius have stayed in the running throughout.
Intrade, Paddy Power and Betfair all listed Joe Biden, Even Bayh and Tim Kaine as their top three favourites on Thursday. Ladbrokes had Hillary Clinton pipping Kaine to third place.
Ken Robertson of Paddy Power said the vice-presidential race had so far accounted for one seventh of all turnover on the company's US presidential betting market.
Hillary Clinton appeared to be one of the biggest losers on Paddy Power's books, he said, due to the high level of early support for her.
Republican candidate John McCain is not expected to pick his running mate until after the Democratic Convention, with next Friday, 29 August, thought to be the most likely date.
The frontrunners are Mitt Romney and Tim Pawlenty.
Tom Ridge, Joe Lieberman, Sarah Palin, Charlie Crist and Rob Portman also feature prominently.
Mike Smithson of politicalbetting.com said Barack Obama had been deliberately "whipping up" excitement regarding his VP choice, by encouraging people to register to receive his announcement by text message. More than a million have done so.
This was a dangerous strategy, he said, because it led them to expect something sensational. A predictable choice, such as Joe Biden, could seem like a let-down.
But the fact that Biden is the bookmakers' favourite may not be as significant as it seems.
According to Tom Snee of the Iowa Electronic Market, at Iowa University, futures markets need more hard information than they get in the veepstakes, to reliably predict a result.
Markets are very good at predicting elections, he says - but not choices being made inside Barack Obama's or John McCain's head.