We made a small acquisition at the end of December, Rio Guayas, the fourth largest non-life insurer in Ecuador. The addition will complement our existing business in that country in terms of geographic presence, product and distribution. By the way, we also closed on Penn Millers in the fourth quarter, a quarter earlier than we had estimated.
Let me talk about the full year and put ACE’s performance for the year in perspective. Full-year net operating income was nearly 2.4 billion, down 11% from 2010. The composition of our operating income was quite good with about one-third coming from underwriting income and two-thirds from investment income. Our results included almost 500 million more in pre-tax catastrophe losses, or twice as much as we experienced in 2010. Excluding the impact of cats from both years, operating income was actually up 5% over prior year. Both years included roughly the same amount of prior period reserve development, so that underlying growth in income came from current accident year results, predominantly from the acquisitions we made as well as our A&H business and improved P&C portfolio management in the U.S.
In 2011, the expense ratio declined over two points year-over-year, and we finished with a P&C combined ratio of 94.6, a very good result when compared to the industry which ran well in excess of 100% in the worst cat year in history globally for the industry. Per share book value grew 6% for the year, bringing three-year growth to almost 19% and five-year growth to over 11.5.
We concluded the year with a very strong capital position. Total capital at December 31, stands at 29.4 billion and shareholder equity at 24.5, both up about 1.5 billion for the year. Our operating ROE for the year was almost 11%, a good result given the cat losses we incurred.