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The Rubicon Project Inc.(NYSE: RUBI) sold 6.77 million shares in an initial public offering (IPO) Wednesday morning. The stock went out at $15 a share, the low end of the expected range, and had gained more than 40% to trade at $21.20 in the mid-afternoon.

Rubicon offers an automated platform for the buying and selling of digital advertising. Of the shares included in the IPO, 5.42 million are being sold by the company and 1.35 million are being sold by existing shareholders. The company expects to receive about $81.3 million gross proceeds.

Underwriters include Morgan Stanley, Goldman Sachs, and RBC Capital Markets, and have been granted an overallotment option to purchase an additional 1.02 million shares.

Revenues totaled $83.8 million in 2013 and the company posted a net loss of $9.2 million. In 2012 Rubicon posted a net loss of $2.4 million on revenues of $57.1 million. In 2011 revenue totaled $37.1 million and the net loss came to $15.4 million.

After the offering the company will have 26.56 million shares outstanding, valuing the company at around $400 million following the IPO. Among the company’s selling investors is News Corp. (NASDAQ: NWSA) which held a pre-IPO stake of 19.3% . News Corp. was expected to sell about 850,000 shares in the IPO, reducing its stake to 13.7%. Following the IPO previous stockholders will own about 43.5% of the company’s common stock.

Other IPOs due this week include GrubHub and Opower, among several others.

Shares are trading up $20.29 in the mid-afternoon on Wednesday, after opening at $17.50, about 17% above the IPO price.