By Nick Timiraos

Interactive: Inventory and asking prices in major metro markets

The number of homes listed for sale at the end of 2012 stood at the lowest level in more than five years, a development that helps explain why home prices have rebounded so strongly over the past year.

The 1.57 million homes listed for sale at the end of December was down by 6.5% from November and by 17.3% from one year ago, according to data tracked by Realtor.com.

Inventories typically decline in December, January and February as home-shopping activity cools. But the big story of 2012 was that inventories never really picked up, despite big declines in the previous year.

“It’s been a buyers’ market for a while. Sellers have been reluctant to put their homes on the market,” said Steve Berkowitz, chief executive of Move Inc., which operates Realtor.com.

January and February, he says, “are going to be an interesting time to watch” because they’ll provide early clues about buyer traffic and sellers’ expectations. Already, online search demand is up from one year ago. “The demand side is showing signs of good things to come,” said Mr. Berkowitz.

Inventories were down in all of the nation’s 30 largest housing markets, compared for 2012 as a whole, led by a jaw-dropping 68% decline in Sacramento, Calif. Other markets with big year-over-year declines included Seattle (45%); San Francisco (43%); Los Angeles (40%); Orange County in California and Atlanta (39%); and San Diego (38%).

Median listing prices were mostly unchanged from one year ago, with declines in just five markets: Cleveland, New York, Philadelphia, St. Louis and Charlotte. Median listing prices posted the largest annual gains in Sacramento, San Francisco, Phoenix and Atlanta.

A separate report on Tuesday from data firm CoreLogic sa id that U.S. home prices gained by 7.4% in November from one year earlier. It projected that home prices would end the year up 7.9% once all of December’s sales data had been tallied.

The Realtor.com figures include sale listings from more than 900 multiple-listing services across the country. They don’t cover all homes for sale, including those that are “for sale by owner” and newly constructed homes that aren’t always listed by the services.

Follow Nick @NickTimiraos