Aon Study: Property & Casualty Earnings Volatility Lower in 2003 than 2002.

CHICAGO -- Aon Corporation (NYSE:AOC) announces today the results of its 2003 Property and Casualty Earnings Volatility Study that highlights the insurers and reinsurers that were most effective at minimizing earnings volatility. Consistent with the results from prior years, the 2003 study indicates

The study measures earnings volatility on a cumulative basis over the one, two, three and five-year earnings periods ending December 31, 2003. The study includes more than 60 public companies within commercial lines, specialty lines, personal lines and reinsurance.

"Once a year we want to recognize the companies that led their respective sectors in generating the least volatile earnings," said Michael Bungert, president of Aon Re Global, the world's largest reinsurance brokerage. "Research on this topic is limited in availability and we are pleased to have published our analysis on an annual basis over the past several years."

The leaders and runners-up by sector and measurement period are as follows:

2003 P&C Earnings Volatility Study Results

One Year    Two Year   Three Year  Five Year
                    Period      Period      Period      Period
                  ---------- ------------- --------- -------------
Commercial Lines:

 Least Volatile     ACE       Hartford     Old Republic      AIG

 Runner-up          AIG          AIG         AIG         Old Republic

Specialty Lines:

 Least Volatile     RLI   Baldwin & Lyons    RLI          RLI

 Runner-up         United       RLI          HCC          HCC
                   Fire &
                  Casualty

Personal Lines:
                   Mercury
 Least Volatile    General      ALFA        ALFA        ALFA

 Runner-up         Direct
                   General      Erie        Erie        Erie

Reinsurance:

 Least Volatile   Montpelier Re  IPC Re     IPC Re    Everest Re

 Runner-up        Everest Re RenaissanceRe Everest Re Transatlantic Re

On a year-over-year basis, earnings volatility for all of the companies included in our study, on average, was 18% lower than 2002. Earnings reflected solid underwriting results stemming from prior rate increases and only marginally higher catastrophe losses. On a relative basis, earnings volatility in 2003 was the lowest in personal lines in three of the four measurement periods compared with the other sectors, consistent with the results published last year.

2003 Sector Volatility Study Results

                        One Year    Two Year   Three Year   Five Year
                         Period      Period      Period      Period
                       ----------- ----------- ----------- -----------

                        Personal   Reinsurance   Personal    Personal
    Least Volatile        Lines                    Lines       Lines

                                    Personal   Commercial  Commercial
    1st Runner-up      Reinsurance    Lines       Lines       Lines

                       Specialty   Specialty   Specialty
    2nd Runner-up         Lines       Lines      Lines    Reinsurance

                       Commercial  Commercial              Specialty
    Most Volatile         Lines      Lines     Reinsurance    Lines

The 2003 study also included, for the first time, rankings based on return on equity (ROE). Over 90% of this year's leaders and runners-up also placed in the top half of the ROE rankings for their respective sectors. The weighted average ROE for all of the insurers and reinsurers in the 2003 study improved to 10.9% from 6.5% in 2002 and 3.5% in 2001.

2003 Sector ROE Volatility Study Results

                                  2003    2002    2001   2000    1999
                                  -----   -----   -----  -----  ------

    Commercial Lines               9.7%    7.3%    3.5%  12.8%   11.5%
    Specialty Lines               14.4%    7.3%    3.4%   1.1%    6.5%
    Personal Lines                 6.5%    3.9%    9.6%  13.8%   16.3%
    Reinsurance                   13.1%    7.6%   -2.7%   6.4%    3.3%

    All Companies                 10.9%    6.5%    3.5%   8.5%    9.4%

Aon Re Global provides traditional, alternative risk transfer and capital markets-based reinsurance advisory and execution services to insurers and reinsurers. Client advisory services include rating agency capital modeling assistance, capital allocation and optimization services, catastrophe modeling services, regulatory assistance, tax analysis, dynamic financial analysis, and capital markets structuring and placement services.

Aon Corporation (www.aon.com) is a leading provider of risk management services, insurance and reinsurance brokerage, human capital and management consulting, and specialty insurance underwriting. The company employs approximately 53,000 professionals in its 600 offices in more than 120 countries. Backed by broad resources, industry knowledge and technical expertise, Aon professionals help a wide range of clients develop effective risk management and workforce productivity solutions.

This press release contains certain statements relating to future results, which are forward-looking statements as that term is defined in the Private Securities Litigation Reform Act of 1995. These forward-looking statements are subject to certain risks and uncertainties that could cause actual results to differ materially from either historical or anticipated results, depending on a variety of factors. Potential factors that could impact results include the general economic conditions in different countries around the world, fluctuations in global equity and fixed income markets, exchange rates, rating agency actions, resolution of regulatory issues, pension funding, ultimate paid claims may be different from actuarial estimates and actuarial estimates may change over time, changes in commercial property and casualty markets and commercial premium rates, the competitive environment, the actual costs of resolution of contingent liabilities and other loss contingencies, the heightened level of potential errors and omissions liability arising from placements of complex policies and sophisticated reinsurance arrangements in an insurance market in which insurer reserves are under pressure, and the timing and resolution of related insurance and reinsurance issues relating to the events of September 11, 2001. Further information concerning the Company and its business, including factors that potentially could materially affect the Company's financial results, is contained in the Company's filings with the Securities and Exchange Commission.