NEW YORK (CNNMoney.com) -- July is shaping up to be the worst month so far this year for companies going public, based on their average-first day performance.

The 15 firms that have launched initial public offerings so far this month have averaged a loss of 0.2 percent on their initial day of trading, according to deal tracker Dealogic.

That would make July the only month so far this year in which the average first-day trading performance for IPOs has fallen into negative territory.

The companies coming to market haven't necessarily been bad, said Irv DeGraw, a Sarasota, Fla.-based researcher of initial public offerings. "It's just a classic reflection of the market going up and down like mad," he said.

Turbulence in the stock market has taken its toll. Only four firms this month -- Indian outsourcing firm WNS (Charts), Chart Industries (Charts), GeoMet (Charts) and Allied World Assurance (Charts) -- have posted gains on the first day of trading.

This week, four firms are set to make their market debut. Here's a look at what's on tap:

Asset Capital Corp. plans to offer 9.3 million shares - 1.25 million of which will be sold by current shareholders. The commercial real estate firm deals in properties in and around Washington.

The company expects shares to price between $9 and $10 a share and plans to trade on the Nasdaq under the ticker "ACCI."

Buckeye GP Holdings LP is offering 14.1 million units in an initial public offering. The company owns and controls the general partner of publicly traded limited partnership Buckeye Partners LP (Charts).

The units represent limited partner interests in Buckeye GP Holdings. Units trade like ordinary shares, but limited partners don't have the same rights typical shareholder do. For instance, they don't have any real ability to influence management.

But these limited partnership offerings generally include generous cash payments. Buckeye GP, for example, intends to make a quarterly cash distribution of $0.205 per unit for the next four quarters.

Buckeye GP Holdings expects its units to price at an estimated range of $19 to $21 a unit. They will trade on the New York Stock Exchange under the ticker "BGH."

Osiris Therapeutics uses stem cells to develop medical treatments. The Baltimore, Md.-based company has developed a treatment that helps bone regenerate and has three other drugs in the pipeline.

Osiris aims to sell 3.5 million shares at an estimated range of $11 to $13 a share. It expects to list on the Nasdaq under the symbol "OSIR."

Security Capital Assurance sells insurance for financial products. The company covers fixed income and other investments that carry the risk of default by the borrower.

About 22.4 million shares will be offered -- the Bermuda-based firm plans to offer 18 million shares, and existing shareholders will sell 4.4 million shares. The company expects shares to price between $21 and $23 a share. It plans to list on the Big Board under the symbol "SCA."

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