Norfolk Southern Corp., the fourth- biggest U.S. railroad, followed Massachusetts Institute of Technology in selling 100-year bonds this month as investors snap up yields above 5 percent on investment-grade debt.

Norfolk Southern sold $400 million of 6 percent debt due 2111 to yield 175 basis points more than 30-year Treasuries, according to data compiled by Bloomberg. MIT, the school founded by William Barton Rogers in 1861, sold $750 million of taxable 5.6 percent 100-year bonds on May 11 at a 130 basis-point spread, Bloomberg data show.

Borrowers are tapping the market for funding that exceeds the average life expectancy in the U.S., which is about 79 years according to World Bank figures, as investors seek higher returns than on typical investment-grade securities. The average yield on an investment-grade corporate bond fell to 3.75 percent yesterday, the lowest since November, according to Bank of America Merrill Lynch index data, making longer-maturity debt more attractive.