Publicis Groupe media shop Starcom MediaVest Group has racked up a lot of digital deals over the past few year, but the agreement it has struck with production firm BermanBraun has the potential to be one of the biggest, according to stories in the NYT and AllThingsD.

The deal could be worth $100 million in ad spending over the next four years. Under the terms of the arrangement, Starcom would get a “first look” at the various online content sites that BermanBraun operate, including the producers’ partnership with MSN on Wonderwall.com and Glo.com, as well as the forthcoming political entertainment site for MSNBC.com and a site for Latinos. Longer term, BermanBraun are working on movie and television portals.

While Starcom gets a first look at the ad placements and content, the deal is by no means exclusive, as BermanBraun can still sell ad inventory across its sites to Stacom rivals. But being first in line, and having a hand in selecting ad formats, is a major advantage.

“Our clients are rightfully demanding a more robust pipeline of digital programming options beyond what exists,” Starcom CEO Laura Desmond tells the NYT. “It is essential for us to help curate and create the content that will fill this gap.”

Publicis Groupe vet Brian Terkelsen, the president of Starcom’s branded entertainment unit, LiquidThread, will manage things from the agency’s end. He expects the collaboration to yield “advertainment” similar to that of the Thread, a celebrity-style show on Yahoo’s Shine portal that features various Procter & Gamble brands.

For BermanBraun, the deal is huge. Instead of having to struggle to find a steady revenue stream, the Starcom deal will ease a lot of that pressure—especially since it will likely attract rivals hoping for good placement.

Still, branded entertainment is one of those nebulous areas of advertising, where effectiveness is hard to measure. The basic rule is that if viewers stick with a piece of content for more than a few minutes, that equals engagement. But for most advertisers, even P&G, it’s still an interesting experiment and considered a big gamble.

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