The number of U.S. homes listed for sale in September rose from the previous month for the 9th straight month, according to data released by real estate brokerage ZipRealty.

The trend is in stark contrast to last year when home price declines kept many potential home sellers sidelined, according to Emeryville, California-based ZipRealty.

Homes are sitting on the market longer and more inventory could add to existing pressures on home prices. Stabilization of the hard-hit housing market, where the recession took root, is seen as key to economic recovery in the United States.

The total number of single-family homes and condos listed for sale by the Multiple Listing Service (MLS) increased in September by 0.60 percent from August, bringing the number of active listings in the 26 major U.S. metropolitan markets to 675,872, ZipRealty reported.

On a year-over-year basis, housing inventories increased by 13.48 percent, it said.

There just were not a lot of homes for sale at this time last year in many markets around the country, said Leslie Tyler, vice president of marketing at ZipRealty. For example, prices had fallen so dramatically in California last year that many sellers would not or simply could not list their homes at those prices.

Now, we are seeing sellers in California adjust to the new market realities and prices are beginning to stabilize, she said.

While low rates and high affordability helped the market to gain ground over the past year, it has struggled since the April 30 expiration of popular homebuyer tax credits.

To take advantage of the tax credits, buyers had to sign purchase contracts by April 30. Contracts originally had to close by June 30, but that was extended by three months.

In other markets, like many in Florida, we are actually seeing fewer homes on the market than at this time last year, which may be a stabilizing force there, she said.

Inventory increased in many markets, while some markets experienced a drop in inventory, according to ZipRealty's Housing Inventory Index for September, which is compiled from local MLS data.

ZipRealty said some of the markets with the most significant month-over-month inventory increases include Las Vegas, Nevada which was up 5.3 percent; and Phoenix, Arizona, which was up 4.2 percent.

Markets with the most significant year-over-year increases also include Las Vegas and Orange Country, up 36.9 percent and up 49.0 percent respectively, the company said.

(Reporting by Julie Haviv, Editing by Chizu Nomiyama)