I don't know how betting works . I'd have thought since one of the two is guaranteed to happen, the odds for one would be the inverse of the other. (Guess not.)

If you put $3 down on Romney and he wins, you get that back plus $7.

That's free money!

So they don't pay you back quite as much as you'd expect for what they think is the true probability of a win.

For those odds of 2/9 and 10/3, to know exactly what you'd get back if you bet on both candidates, you'd have to bet £117 on Obama (9x13 - you win 2x13=£26, and get the £117 back) and £33 on Romney (3x11 - win 10x11=£110, and get the £33 back). But that means you've staked 117+33=£150, while you'll get back £143. There's the bookie's profit.

Page to show all the major UK bookies current odds here: http://www.oddschecker.com/specials/politics-and-election/us-presidential-election/winner

Ladbrokes is now Obama 1/5, and some are even further - 2/13. Every single one shows blue, ie they have recently alerted their odds to say Obama victory is getting more likely.