The 100 biggest publicly traded U.S. companies with defined benefit pension plans ended the first quarter with about 100% of the assets they need to cover their pension liabilities.

The companies, which have about $19 billion in annual pension costs and $1.3 trillion in pension plan assets, ended 2007 with an overall funded status of 106%, up from 99% a year earlier, according to researchers at Milliman Inc., Seattle.

The gains vanished in the first quarter of the current year as a result of asset losses and a drop in interest rates, the researchers write in a commentary on the results.