American Express announced Tuesday that its prepaid debit cards will now be backed by the Federal Deposit Insurance Corp., the latest indication that a market once shunned by established financial institutions is gaining ground. The use of reloadable prepaid cards

The Russell family of Kirkland, Wash., makes about $230,000 with Charles Russell, 43 years old, working as a systems analyst for Microsoft Corp. According to the U.S. Census Bureau, that puts them among the top 5% of American households. But their affluence might not be apparent based on the way Mr. Russell conducts his personal finances. He has no bank account, having dumped it due to irritation over fees and overdraft penalties. Instead, for more everyday transactions he uses a debit-card offered by NetSpend Holdings Inc.