It's the best of times, it's the worst of times for pension holders of United Parcel Service of America.

In this tale of two pension plans, if the employees are among UPS's 125,000 nonunion workers, they're in fine shape. Big Brown's $10.5 billion in-house plan is one of the rare corporate schemes to be overfunded, boasting $110 in assets for every $100 in liabilities. Its portfolio returned 13.3 percent in 2004 -- the most recent year for which figures are available -- and an annualized 10.9 percent for the three years ended 2004. Those results handily best the 12.2 percent and 7 percent returns, respectively, for plans of the nation's 100 biggest corporations, according to Seattle-based Milliman Consultants.

However, if a UPS employee happens to be among the company's 220,000 unionized employees -- more than half of them drivers -- who are covered by one of Big...