Buffett referred to this group of companies as Berkshire Hathaway's "Big Four." Berkshire invested $3.83 billion in the four through mulitiple transactions between May 1988 and October 2003; on a composite basis, Berkshire's dollar-weighted purchase data was July 1992. By year-end 2004, Berkshire held these interests, on a weighted basis, for about 12.5 years.