The document summarizes the primary holdings of the world's top four agency companies by 2009 worldwide revenue:
1) WPP had $13.6 billion in worldwide revenue and holdings include Grey Group and other marketing services agencies.
2) Omnicom Group had $11.72 billion in worldwide revenue and holdings include specialty communications agencies and traditional media advertising.
3) Publicis Groupe had $6.29 billion in worldwide revenue and holdings are led by its media agency Starcom Mediavest Group.
4) Interpublic Group had $6.03 billion in worldwide revenue and holdings include advertising and media agencies such as Lowe & Partners.