Tremor Video, which comScore reports is the largest independent video ad network, has added an additional $37 million to the approximately $78 million in funding it already raised. At least half of the money will be used for acquisitions and for expanding its presence in Europe beyond the U.K. and Germany.

Tremor already purchased mobile video ad network Transpera and a potential competitor, ScanScout, during the past year, according to AdAge. The funding also will be useful for expanding Tremor’s Video Hub analytics platform and making it available as a freestanding product in addition to its current use by Tremor Video clients.

The new round was led W Capital Partners, with participation from Keating Capital, Canaan, Draper Fisher Jurvetson Growth, General Catalyst, Meritech, Singapore’s EDBI, Time Warner and SAP Ventures. Bob Migliorino, managing director of W Capital Partners, will take a take a seat on Tremor’s board.

Keating Capital’s involvement adds to predictions of a flotation, since the company specializes in pre-IPO investments. “According to eMarketer, a digital marketing research firm, the U.S. online video advertising market is estimated to be approximately $2.2 billion in 2011 growing to nearly $5.7 billion by 2014, with video ads representing about 29 percent of the projected $19.6 billion U.S. online display advertising market in 2014 second only to banner ads with 56 percent of the market,” Keating Capital’s CEO Timothy J. Keating said in a statement. “We believe Tremor Video is one of the pioneers leading the development and transformation of the online advertising industry, and we are delighted to be an equity capital partner with the company.”

Tremor Video places video advertisements before or next to online videos or other content for brand advertisers such as Procter & Gamble, Mars, Microsoft, Sprint Nextel and Walt Disney. The company provides advertisers with tools to target and engage customers, measure campaign effectiveness and ensure brand safety by scanning and categorizing each video stream before an advertisement is placed.

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Image courtesy of Tremor Video