Buffett referred to this group of companies as Berkshire Hathaway's"Big Four". Berkshire invested $3.83billion in the four through multiple transactions between May 1988 and october 2003; on a composite basis, Berkshire's doller-weighted purchase date was July 1992. By year-end2004. Berkshire held these interests, on a weighted basis, for about 12.5years. Source of data: Berkshire Hathaway lnc., 2004 annual Report, 16.