X0202 4 2006-05-03 0 0000947484 ARCH CAPITAL GROUP LTD. ACGL 0001162870 WARBURG PINCUS LLC 466 LEXINGTON AVENUE NEW YORK NY 10017 0 0 1 0 0001157334 WARBURG PINCUS PRIVATE EQUITY VIII L P 466 LEXINGTON AVENUE NEW YORK NY 10017 0 0 1 0 Common Shares, $0.01 par value per share 2006-05-03 4 J 0 4028333 D 18882145 I Partnership THE SECURITY HOLDERS ARE WARBURG PINCUS (BERMUDA) PRIVATE EQUITY VIII, L.P. ("WP VIII BERMUDA") AND WARBURG PINCUS (BERMUDA) INTERNATIONAL PARTNERS, L.P. ("WPIP BERMUDA") AND WARBURG PINCUS NETHERLANDS INTERNATIONAL PARTNERS I, C.V. ("WPIP NETHERLANDS I"). WARBURG PINCUS (BERMUDA) PRIVATE EQUITY LTD. ("WP VIII BERMUDA LTD.") IS THE SOLE GENERAL PARTNER OF WP VIII BERMUDA. WARBURG PINCUS (BERMUDA) INTERNATIONAL LTD. ("WPIP BERMUDA LTD.") IS THE SOLE GENERAL PARTNER OF WPIP BERMUDA. WARBURG PINCUS PARTNERS, LLC IS THE SOLE GENERAL PARTNER OF WPIP NETHERLANDS I. WP VIII BERMUDA, WPIP BERMUDA AND WPIP NETHERLANDS I ARE MANAGED BY WARBURG PINCUS LLC ("WP LLC"). CHARLES R. KAYE AND JOSEPH P. LANDY ARE MANAGING MEMBERS AND CO-PRESIDENTS OF WP LLC AND MAY BE DEEMED TO CONTROL THE WARBURG PINCUS ENTITIES. ON MAY 3, 2006, THE REPORTING PERSONS DISTRIBUTED AN AGGREGATE OF 4,028,333 COMMON SHARES OF THE ISSUER TO THEIR LIMITED AND GENERAL PARTNERS. /s/ Scott A. Arenare, Managing Director 2006-05-05