Supply and demand image via Shutterstock.

Editor’s note: Data collected and analyzed by Realtor.com through  May 2012. Includes single-family homes, condos, townhomes and co-ops.

The national housing market continues to stabilize, according to data compiled by Realtor.com for 146 U.S. metros through May 2012.

May continued April’s year-over-year upswing, with for-sale inventory dropping 20.07 percent, median list prices jumping 3.17 percent to $194,900, and median age of for-sale inventory falling 9.78 percent compared to a year ago.

As of May, national for-sale inventory stood at 1.88 million units, roughly 60 percent of a September 2007 inventory peak of 3.1 million units (2007 was the first year Realtor.com tracked this data nationally).

Despite a slight 1.96 percent month-over-month increase in national inventory — expected because listings usually swell during the springtime buying season — all but two of the 146 metros Realtor.com tracks had fewer homes for sale than a year ago.

Some of those markets hit hardest in the housing crisis — Atlanta and metros in Florida, Arizona and California — are showing some consistent, month-by-month turnaround. In May, Phoenix, Tampa-St. Petersburg, Fla., and Atlanta were among the top 10 metros Realtor.com tracks with year-over-year percentage drops in for-sale inventory.

This month, six of the metros in the top 10 that saw the greatest reduction in inventories from a year ago were in California, including three in the San Francisco Bay Area: Oakland at No. 1 (56.6 percent fewer listings than a year ago); San Jose at No. 6 (40.88 percent fewer listings); and San Francisco at No. 10 (38.9 percent fewer listings).

Top 10 metros for greatest year-over-year reduction in for-sale inventory, May 2012