March ended with the estimated inventory at 5.5 months, meaning it would take that long for all the houses listed for sale to be sold if no more went on the market. Realtors generally consider a supply of between five and six months to give buyers and sellers basically equal footing in negotiations.

The Oklahoman estimated the inventory by dividing the average monthly sales for the past year by the number of houses for sale at the end of March, using statistics from the Oklahoma City Metro Association of Realtors. The numbers include only sales handled by Realtors, not houses sold directly by owners or builders.

Realtors handled the sale of 1,485 houses in March, 18.6 percent more than in March 2011, at an average price of $157,157, according to the association. Sales were fueled partly by low mortgage interest rates, which averaged 4.08 percent in March, the Realtors reported.

“March (had) all positive numbers,” said Lorna Koeninger, president of the Metro Association of Realtors and an associate at Paradigm AdvantEdge Real Estate. “The inventory is still down, keeping at under a six-month supply, although the listings during March were at a 10-percent increase over last year.”

It has set the stage for a successful Nationwide Open House Weekend 2012. The National Association of Realtors counted 31,078 “open house events” this weekend. Friday, about 230 houses were listed as open this weekend on www.centraloklahomaproperties.com, a website of the metro-area Realtors Multiple Listing Service.