Irrational Games' 2007 hit BioShock has now exceeded 4 million units sold, according to publisher Take-Two -- and part of that success was spurred by 2K Marin and 2K Australia's just-released sequel, BioShock 2. In a conference call following the announcement of a successful first quarter, company CEO Ben Feder said the BioShock series has sold 7 million units combined, with BioShock selling 4 million units and BioShock 2 shipping 3 million so far. "We've seen an impact on our BioShock 1 catalogue [sales] as a result of BioShock 2," Feder explained. "We're pleased with it." CFO Lanie Goldstein said Take-Two saw a considerable boost to its digital distribution revenue, which jumped from 3 percent of the publisher's business to 12 percent year-over-year. That digital distribution growth and the increase in BioShock sales -- last time the company gave sales figures on the game, it had sold only 3 million units -- could be partially connected. Feder said that in addition to stronger-than-expected performance of Borderlands downloadable content, sales of older catalogue titles drove digital growth considerably. And a recent pre-order deal packaging four copies of BioShock 2 with four copies of BioShock on Valve's Steam PC distribution service retained a high position on the Steam sales charts during the time of its release. As for financial expectations of BioShock 2's upcoming DLC, Feder declined to comment in detail, but he did say the company is optimistic. "We think the DLC is providing value to our consumers," he said. "We think consumers like it and want it." [UPDATE: Take-Two revealed additional sales and shipping figures during its earnings call. June 2008's Grand Theft Auto IV has sold 15 million units to date, NBA 2K10 has shipped 2 million, and Carnival Games has sold 6 million units.