Bangor has been a successful guinea pig, now Portland wants an outdoor venue.

Portland saw success two years ago in bringing Grammy award winning act Mumford & Sons to town. 15,000 fans converged on Portland’s Eastern Promenade for the show. Now two proposed sites for an outdoor amphitheater are starting to get the ball rolling.

One site is along the banks of the Presumpscot River in Westbrook's Riverbank Park. The Portland plan is a lot adjacent to Bug Light Park. The lot is owned by developer John Cacoulidis. Portland's venue is expected to be seat 10,000 people, while Westbrook's will seat 2,500.

Westbrook's planners formally unveiled their idea this week, while Portland will do so Tuesday. Organizers say only one venue will likely succeed, and that venue will be the one that's completed first.

A 2012 study by a University of Maine economics professor showed Bangor's concert venue has brought $30 million to the area. The University of Southern Maine also looked into the idea of concerts bringing more money to the Portland area. They found the shows could infuse $7 million into the local economy.

Both planning committee's say they have been working with unidentified concert promoters.