Seattle casual games powerhouse Big Fish Games is paying up to $15 million to purchase an undisclosed privately-held corporation. An SEC filing reveals that Big Fish today issued shares tied to the purchase, though the name of the company it acquired was not disclosed.

“The total offering amount includes up to $3,412,800 of equity that may be issued and sold upon the satisfaction of certain earn-out provisions under the merger agreement between the issuer and a privately-owned corporation,” the filing says.

We’ve reached out to executives at the company, and we’ll update the post as we hear more. Founded 10 year ago by former RealNetworks employee Paul Thelen, Big Fish has been expanding into mobile and social gaming realms in recent months.

Last month, Big Fish purchased Self Aware Games, a 23-person Oakland, California company that makes the mobile casino game Card Ace: Casino. It’s unclear whether today’s SEC filing is connected to that acquisition, or represents another deal. The terms of the Self Aware Games purchase were not previously disclosed.

Big Fish is profitable and growing, with revenue of $140 million in 2010. It said that revenue grew by about 30 percent last year, marking the ninth consecutive year of record revenue growth.

It raised an $83 million venture capital round in 2008 from Balderton Capital; General Catalyst Partners; and Salmon River Capital.

UPDATE: A spokeswoman for Big Fish said that the SEC filing does not indicate new funding, and that the filing is connected to the purchase of Self Aware Games.

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