Yup. Typically, a $1000 over/under bet will cost you $1100. (Your bet plus a 10% vig). Let's assume one person bets the over for a thousand, one bets the under, also for a thousand. Vegas has collected $2200. If you lose, they keep the $1100. If you win, you get $2100. Nice little system they got...if they can just get an even amount of money on either side, they use the losers bet to pay the winner, the winner gets his money and vig back, but Vegas keeps the vig from the loser. They are guaranteed a profit of almost 5% of the total bet on both sides, minus their overhead of course. That theory works a lot better on single events than it does on things like "over/under" team win totals, though. In theory, if Vegas can hit the sweet spot on the spread for a game, they can't lose. Even amount of money bet on both sides, it doesn't matter which team wins. Vegas gets its 5%. But, at least in theory, Vegas could lose money on EVERY team on the "over/under." Of course, in theory they could win money on every team, too. Mostly, Vegas doesn't care much for these types of bets, because they have much less control over the outcome. They are pretty good at setting the totals for these kinds of things though, which is why they offer 'em.