www.Zillow.com, an online real estate information provider that estimates housing market values, ranked Honolulu as the second most expensive single-family home market out of 66 U.S. metropolitan areas during the second quarter.

Zillow said the median home value for O'ahu, or Honolulu county, was $632,270 during the April-to-June period. The priciest market was San Francisco-Oakland-San Jose, Calif., at $685,653. A distant No. 3 was San Luis Obispo-Atascadero-Paso Robles, Calif., at $537,722.

O'ahu's estimated median home value was down 3.1 percent from the 2006 second quarter but up 0.2 percent from the first quarter, according to Zillow.

Zillow's estimated values, called Zestimates, are made in part by comparing sale prices of similar homes by area. The estimates are designed to provide a gauge for what homes in a particular area are selling for.

The company said it has data for 68 percent of Hawai'i homes, including some on the Neighbor Islands. Compared with actual sale prices, Zillow figures half its estimates for O'ahu are off by less than 8.2 percent, while half are off by more than 8.2 percent.

The Honolulu Board of Realtors, which puts out data on actual home sales, said the median price of O'ahu single-family homes sold in the second quarter was $665,000, up 3.9 percent from the 2006 second quarter and up 7.3 percent from the first quarter.