Six companies are scheduled to price and begin trading the week of Sept. 21, which could become the busiest for U.S. initial public offerings since December 2007.

The companies are: lithium car battery maker A123 Systems Inc; Swiss bank Julius Baer's U.S. asset management unit Artio Global Investors Inc; Apollo Commercial Real Estate Finance Inc and Colony Financial Inc, both real estate investment trusts; on-line health supplement retailer Vitacost.com, and hospital operator Select Medical Holdings Corp.

All six companies set terms for their IPOs in separate filings with the U.S. Securities and Exchange Commission on Wednesday.

Here are the details for each IPO: COMPANY EST PROCEEDS No OF SHARES PRICE RANGE TICKER EXCHANGE Artio Global Investors $585 mln 23.4 mln $24-$26 ART NYSE* Bookrunners: Goldman Sachs Colony Financial Inc $500 mln 25.0 mln $25 CLNY NYSE Bookrunners: Bank of America, Goldman, Morgan Stanley, UBS Apollo Commercial $400 mln 20.0 mln $20 ARI NYSE Bookrunners: JP Morgan, Citi, Barclays Capital Select Medical Holdings $400 mln 33.3 mln $11-$13 SEM NYSE Bookrunners: Goldman Sachs, Morgan Stanley, Bank of America, JP Morgan A123 Systems $225 mln 25.7 mln $8-$9.50 AONE Nasdaq Bookrunners: Morgan Stanley, Goldman Sachs Vitacost.com $132 mln 11.0 mln $11-$13 VITC Nasdaq Bookrunners: Jefferies & Co, Oppenheimer & Co (* New York Stock Exchange)

(Reporting by Phil Wahba)