Opening a bank account may increase your odds of being able to participate in a lucrative new stock offering.

How? Mutual thrifts — or, as they are more generally known, savings and loans — can offer such an opportunity.

Depositors are the owners of S&Ls. If a thrift's directors decide to convert to stock ownership, anyone who clutches a passbook or owns a certificate of deposit or a checking account is eligible to buy shares — usually at favorable prices — before they begin trading. Outsiders must line up behind depositors.

Eligible depositors pay no fees or brokerage commissions to acquire the shares, and they continue to earn interest on their accounts.

Thrifts offer the potential for serious stock appreciation. From January 2001 through September 2005, the 69 S&Ls that completed initial public offerings registered opening day gains of 20 percent, on average, according to SNL Financial, a banking research firm headquartered in Charlottesville, Va. Over the past decade, new thrift stocks advanced an average of 25 percent in their first quarter of public trading.

Luck plays a role in identifying thrifts that eventually go public. But investors like Bob Yohanan, who has been making deposits locally and by mail for more than a decade, try to improve the odds of finding a winner.

Yohanan, chief executive officer of First Evanston Bancorp, a banking company in Evanston, Ill., looks at a thrift's equity-to-asset ratio (the company's retained earnings divided by its loans and the debt securities it holds). A low ratio suggests that business is good and that the S&L needs capital to keep up with it. One way to raise money is through an IPO.

For Yohanan, an S&L is a good candidate for conversion if the equity-to-asset ratio falls below 15 percent. You can find the figure for each S&L in the FDIC database. Go to www.fdic.gov, click on the "Industry Analysis" tab, then on "Institution Directory" and then on "Find Institutions."

Once you've located the thrift by name, click on the institution's certificate number, then on "Generate Report," and then change the data from "dollars" to "ratios." Because liabilities equal assets, the number for "equity capital" as a percentage of liabilities is the same as the equity-to-asset ratio.

SNL analyst Mike Schaller considers the directors' age. The grayer they are, the more likely they'll be looking to cash out, says Schaller. You can often learn S&L chief executives' ages by scanning any of the various "Who's Who" publications.