The number of homes listed for sale increased in many metropolitan areas in March.

The supply of homes available for sale in 27 major metropolitan areas at the end of March was up 5% from a month earlier, according to figures compiled by ZipRealty, a real-estate brokerage firm based in Emeryville, Calif. The ZipRealty data cover all single-family homes, condominiums and town houses listed on local multiple-listing services in metro areas where the firm operates.

Inventories typically rise modestly in March from the February level as people put houses on the market in anticipation of the busy spring home-shopping season. Over the past 27 years, the average increase in March has been 1.8%, according to Ivy Zelman, chief executive of Zelman & Associates, a research firm.

Compared with the year-earlier month, the March inventory in the 27 metro areas covered by Zip was down about 14%.

Wall Street Journal