There are conflicting reports out about ticket sales for Britney  Spears' Vegas concerts ... some are saying sales are disastrously poor  ... Brit's people are saying "it's the best-selling show in the history of  Vegas."  TMZ now has the numbers, and it's pretty clear -- Britney is about  to own Vegas.

Britney will be performing 48 shows a year for the next 2  years -- according to the contract obtained by TMZ.   Tickets are available  now for the first 16 shows.  We've been on dozens of calls with StubHub,  Ticketmaster and Planet Hollywood's box office among others ... and here's what  we're told.

For the first 16 shows ... a total  of 73,600 tickets were up for sale.  The  number of tickets actually sold are impressive --  70,242.  

Of the available,  remaining, 3,358 tickets, 2,887 are  in the nosebleed section.

We can't vouch for this being the best selling  show ever in Vegas, but it's definitely up there.

Britney sources have  told us they're actually talking about adding shows, and if that happens Britney  will rake in even more than the $15 mil a year she's already guaranteed.

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