I'm pretty sure it's Jill Wagner from the MTV show Punk'd... she was only on for a season or less but I think that is her. Here is her lay out in Stuff Magazine
http://www.stuffmagazine.com/cover_girls/girl.aspx?id=354

> Now she is in the 2005 Mercury Mountaineer commercial!
> I was lucky enough to be able to capture the Montego commercial.
> I am trying to capture the Mountaineer one as well.
>
> She is soooo hot!
> Somebody PLEASE contact Lincoln/Mercury & find out who she is, cos I don't have the time - gotta go.
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