SAN FRANCISCO—San Francisco's residential inventory remains extremely tight, and prices increased again in May, according to the Mark Company Pricing Index. The company released reports for the month of May on San Francisco, Los Angeles and Seattle. In all three cities inventories of resale units are tight, but San Francisco, with just one month's inventory on the market, is the tightest.

For May, San Francisco's average prices were up 1% from April. Prices rose 14% from the year prior.

Pricing Index is the tool for tracking the value of a new construction condominium without the volatility of inventory changes. The Pricing Index uses a proprietary quantitative method to model the price per square foot of a new 10th floor, 1,000 SF condominium.

San Francisco's price index for May was $1,125 per square foot. The Penthouse Pricing Index applies the same methodology to a new 30th floor, 2,000 square foot penthouse. San Francisco's penthouse price index for May was $1,932 per square foot. Resale prices for San Francisco condos were up 18% from a year ago.

In Dowtown Los Angeles, the index was $673, per square feet, and $1,088 for the penthouse index, while Downtown Seattle's number hit $775, and $1,198 for the penthouses. In May Los Angeles had 2.4 months of inventory—still considered low—and Seattle had just 1.8 months.