The betting industry can be difficult to forecast, in part because most gamblers place their bets in the 24 hours preceding the event, but British bookmakers say that they could see more than 1 million pounds ($1.6 million) worth of wagers on the royal wedding.
That's small change compared to what's bet on sports but a hefty sum by the standards of nearly everything else in Britain's betting industry. For example, the figure is 10 times the amount typically staked on "The X Factor," Britain's most-watched TV talent show.
"As a nonsports event that will be second to only our pope-betting in 2005," said Paddy Power spokesman Darren Haines, referring to the election that followed Pope John Paul II's death in 2005.
Britons have been swapping bets on royal foibles for decades -- many gambled on the name Diana would choose for her eldest son -- but recent years have seen an expansion in the scope of the bets offered by mainstream bookmakers.
William Hill has bets out on whether Middleton will get a kiss on the cheek or on the lips when the couple appear at the Buckingham Palace balcony, whether her father will cry as he walks her down the aisle, and whether Prince Harry will catch her bouquet. Among the less likely bets: That the happy couple car's will break down outside Westminster Abbey, that Middleton will jilt William at altar, or that Prince Harry will be too drunk to finish his speech.
That last option pays out 25 pounds for every pound wagered.
It all may sound a bit far-fetched. But in this country's sometimes wacky betting industry, bookies accept wagers and set odds on whatever fanciful idea crops up in a gambler's head -- from predicting showbiz split-ups to the discovery of extraterrestrial life.
Retiree Robert Foster, who was standing outside the abbey, said his "favorite bet" was the wager that William and Middleton would stay together.
"I can't see the car breaking down at all, and I can't really see them parting because they're a good-looking couple," he said.
The whens and the wheres of the wedding -- which produced a surge of betting in the immediate aftermath of the engagement announcement -- have already been settled. But some important questions -- such as the kind of dress Middleton will wear on the day in question -- are still up for grabs, at least at some bookmakers.
Paddy Power's website put the odds of Sarah Burton designing the dress at one to two, meaning that it was twice as likely as not that Burton would be the one chosen by Middleton to design the dress. Other possible designers include Bruce Oldfield and Jasper Conran.
Paddy Power competitor Ladbrokes isn't offering odds on the dress's designer, but royal watchers can still bet on the weather (odds of rain are 3-to-1) or the color of the queen's headgear (yellow is the clear favorite.)
So will gamblers be rolling in the dough? Or do the bookmakers see the wedding as a chance to clean up?
Neither, said Adams. Gamblers were most likely to place "a small bet for a joke," for example by placing 10 pounds on William splitting his trousers or Prince Philip falling asleep. The average royal bets tend to be between 2 pounds and 6 pounds, he said. In contrast, the average soccer bet is about 14 pounds. And unlike a sporting event, where the results can only be guessed at ahead of time, those close to the royals may already know, for example, whether Elton John will sing live or whether Middleton will be wearing red heels as she walks the aisle.
Bookmakers have little choice but to manage their risks, declining suspicious bets or just paying out when a clever insider slips a winning wager through the net.
"We're betting on things, quite a few things that some people know the answer to," Adams said. "If we break even, we'd be happy."
After the wedding, interest in the royal couple will likely wane -- although it won't disappear. Gamblers are already being offered the chance to bet on the names of the couple's children.