X0303 4 2010-12-15 0001141719 ALTERRA CAPITAL HOLDINGS Ltd ALTE 0001047633 COOK ANDREW C/O ALTERRA CAPITAL HOLDINGS LIMITED ALTERRA HOUSE, 2 FRONT STREET HAMILTON, BERMUDA D0 HM 11 BERMUDA 0 1 0 0 EVP, Global Business Dev. Common Shares 2010-12-15 4 S 0 5300 21.526 D 247200 D Common Shares 2010-12-15 4 S 0 700 21.50 D 246500 D Common Shares 2010-12-16 4 S 0 44000 21.42 D 202500 D The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $21.40 to $21.48, inclusive. The reporting person undertakes to provide to Alterra Capital Holdings Limited, any security holder of Alterra Capital Holdings Limited, or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares sold at each separate price within the ranges set forth in footnote (1) to this Form 4. Bernard Asirifi, Attorney-in-Fact 2010-12-17