Beverly Hills-based Platinum Equity tops the Business Journal’s list of the largest privately held companies headquartered in L.A. County for the fourth consecutive year.

Platinum Equity’s portfolio companies totaled $8 billion in 2007 revenues, holding steady from the prior year.

Founded in 1995 by Tom Gores, the firm buys and runs companies in sectors such as information technology, logistics, manufacturing, entertainment distribution and software.

The company has made several transactions this year. In March, it acquired Wheels Pro, a distributor of third-party wheels and tires to the automotive aftermarket. Two months later, it integrated the company with portfolio company American Racing, which it had acquired in 2005.

In April, Platinum acquired Covad Communications in a public-to-private transaction. Covad provides voice and data communications products to consumers and businesses in 235 metropolitan areas in the United States. Also in April, Platinum acquired Owens Corning’s glass-fiber manufacturing facilities in Belgium and Norway. The facilities make glass fibers used to strengthen parts used by manufacturers of automotive, wind energy and electronics components.

In August, Platinum completed the sale of PNA Group to Reliance Steel & Aluminum Co. in a $1.1 billion transaction. Platinum acquired the metal processor in 2006 and the company’s revenue grew from $1.2 billion to $1.6 billion annually under its ownership.

Since inception, the firm has acquired more than 80 businesses.