If successful, Omnicom and Interpublic would become the largest advertising company in the world, with more than $25 billion in combined revenue. Advertising and Marketing, Mergers, Acquisitions and Divestitures, Omnicom Group Inc, Interpublic Group of Companies Inc, Regulation and Deregulation of Industry, Federal Trade Commission, Online Advertising If successful, Omnicom and Interpublic would become the largest advertising company in the world, with more than $25 billion in combined revenue. NYT > Business