The IPO window may be closed, but limited partners still are willing to put some chips on venture capital, a new study says.

In the first half of 2008, U.S. venture capital firms raised $11.5 billion, a 14.8 percent increase over the 2007 period, according to Dow Jones Private Equity Analyst.

The performance of venture capital funds came in stark contrast to leveraged buyout funds, whose high-powered deals made them the toast of Wall Street last year.

The $85.5 billion that limited partners like pension funds and endowments plowed into LBO funds was 20.5 percent below the $107.6 billion invested in the first half of 2007.

“For first time since 2003, we’ve seen year-over-year fund raising actually decline as some of the bigger firms—Blackstone Group, Carlyle Group, and Madison Dearborn Partners—ran into delays raising capital for their latest buyout funds,” Jennifer Rossa, managing editor of Dow Jones Private Equity Analyst, said in a statement.

Seventy-two new venture capital funds raised money, 10 more than in the 2007 period. The largest haul was for the $800 million Lightspeed Venture Partners VIII LP fund.

Alarms have been raised in the venture capital industry because there was not a single initial public offering of a venture-backed company in the second quarter. IPOs are viewed as essential to the health of the industry by providing an avenue for LPs to cash out of a company.

Overall, U.S. private equity firms raised $132.7 billion in the first half, 3 percent less than in the year-ago period.

Declines were recorded for funds of funds (from $11.7 billion to $8.1 billion) and secondary and other funds ($5.7 billion to $3.6 billion).

Mezzanine funds, meanwhile, helped provide ballast with a sharp increase from $2.3 billion in 2007 to $24 billion in 2008. That increase was attributable almost entirely to the $20 billion Goldman Sachs Mezzanine Partners V LP fund.

Though private equity fundraising declined in the United States, Dow Jones reported an uptick in Europe, where investors put $61.1 billion into 80 funds, a 16 percent year-over-year dollar increase.