If you're looking for good news about the housing market, you're going to have to wait awhile longer, as new research continues to paint a grim picture. Nearly 16 million homeowners -- almost one third of all Americans who have a mortgage -- owe more to the bank than their home is worth, according to a report released Thursday by real estate valuation company Zillow. The report is surprising since research released in March by CoreLogic estimated the number of "underwater" homeowners closer to 11 million, or roughly a quarter of all homeowners who have mortgages.

The difference in findings may be due to methodology. Whereas previous estimates rely on public record of home loans, Zillow partnered with credit rating agency TransUnion to get information about second mortgage loans and the portion of the loans that had been paid down, according to the Wall Street Journal.

According to a blog post by Zillow's chief economist Stan Humphries, U.S. homeowners who are underwater owe on average $75,644 more than what their home is worth, and collectively owe a whopping $1.2 trillion more than the value of their homes.

But the problem varies by geography. For example, nationally, less than five percent of these borrowers owe more than twice the value of their home, but in the Las Vegas metro area, it's closer to 25 percent of homeowners. And across Nevada, a stunning two-thirds of all homeowners are underwater, making it the state with the highest percentage of underwater borrowers nationally. Other states with high percentages of underwater borrowers include Arizona (52 percent), Georgia (47 percent), Florida (46 percent) and Michigan (41 percent). (To see how your state compares, check out this map from Zillow).

Underwater homeowners face a number of challenges. For starters, it's hard to sell your home, as you won't be able to get as much as for it as you owe to the bank. As a result, it's difficult to relocate for a better job or cheaper housing. Research indicates these homeowners are also at a higher risk of losing their home to foreclosure, either because they can't afford to keep up with the mortgage or don't see the point in making payments on a home that seems impossible to ever pay off.

And yet, despite the challenges these borrowers face, 90 percent of underwater homeowners continue to pay their mortgage on time, according to the report.

To read stories from underwater homeowners about how the experience has affected them, check out this blog, which is a collection of stories from borrowers. Or if you are currently underwater on your mortgage you can share your story with us by sending an email to: money@huffingtonpost.com.