backlash and a statute change in Delaware which allowed a corporation to amend its charter to eliminate directors' personal liability for violation of the duty of care; a version of this statute has been passed in all states, and most large corporations have such an "exculpatory clause". In some cases scholars propose that the risk of personal liability for corporate officers be increased. Empirical research One empirical study found that increased D&O insurance is associated with reduced shareholder benefits from mergers and acquisitions. Monitoring role Since insurance companies ultimately bear costs for negligent management, theoretically, insurance companies may enforce better management practices and reduce moral hazard. Empirical research, however, has not found that insurance companies perform effective monitoring of management. Berkshire Hathaway Berkshire Hathaway, the holding company managed by Warren Buffett, does not purchase D&O insurance for its directors, unlike most similar companies. Warren Buffett believes that the directors should face consequences of their mistakes the way that other shareholders do. Notably, however, this statement overlooks the holding-company structure of Berkshire Hathaway, auxiliary indemnification agreements with Buffett, and the individual operating companies may still purchase such insurance. Market size and vendors In the United States, total direct premiums written amounted to about $2.9 billion from 2013 to 2014, with Axa XL as the market leader with 15% market share according to analysts at Fitch Ratings. The leaders in the provision of directors and officers liability insurance include Axa XL, AIG, Chubb Limited, Tokio Marine HCC, The Travelers Companies, CNA Financial, Berkshire Hathaway, and Sompo Group via Sompo Japan Nipponkoa Insurance, among many others. In the United Kingdom, the majority of contracts are facilitated on behalf of policyholders by intermediary brokers. External links The ABCs of D&O Insurance Clauses References Bandle, L'assurance D&O (with English and German abstract), Lausanne, 1999 Mannsdorfer, Die sonstigen, uebrigen oder allgemeinen Bestimmungen in der D&O-Versicherung (with German and French abstract), HAVE 3/2010, 222-247 Corporate directors Liability insurance Types of insurance