U.S. insurers are buying corporate pension plans at a record clip as rising interest rates and all-time high stock-market values give companies the perfect excuse to offload them. Calculating they can make more money from selling companies an annuity to cover the cost of the pension plans and then invest the proceeds in bonds and other securities, insurers are competing to persuade corporate America to sell them their pension risk. "There's a huge opportunity for the insurance industry," said Ellen Kleinstuber, who advises pension-plan sponsors as an actuary for CBIZ Inc .