Detroit's July plunge into bankruptcy illustrated the financial vulnerability of U.S. cities. While most are much better off than the Motor City is, many municipalities face a range of problems.

That includes increasing pension and healthcare expenses, weak revenue from property taxes and large cuts in state aid, according to The Wall Street Journal.

Merritt Research Services analyzed 2012 financial filings for almost all of the nation's 250 biggest cities.

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Some of the results weren't encouraging. For example, reserves for more than half of the cities in 2012 were at levels below 2007, prior to the financial crisis, The Journal reports. In addition, 114 cities experienced an increase in their debt from 2007 to 2012.

Meanwhile, in 100 cities, the real estate markets remained worse last year than in 2007. That makes a big difference for cities, as they depend on property taxes as a major source of revenue.

The 2008-09 financial crisis "thinned the cushions," Merritt CEO Richard Ciccarone tells The Journal. "The weakest of the cities haven't rebuilt their balances."

Moody's Investors Service says, "More local governments today are facing heightened long-term fundamental credit challenges than at any time in the recent past," the paper reports.

But with the municipal bond default rate below 1 percent, many experts express confidence in that market.

"More than 99.5 percent of bonds are safe, but that just gets buried when people are worried," Rafael Costas, co-director of Franklin Templeton’s municipal bond department, tells The New York Times.

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