American commercial real estate prices may fall as much as 15% over the next year in the broadest decline since the 2001 recession as rising borrowing costs force property owners to accept less or postpone sales.

“People aren’t willing to do deals right now,” the New York-based chairman of Carlton Advisory Services Inc., which has arranged financing for real estate purchases including the Lipstick Building in midtown Manhattan, Howard Michaels, said. “The expectation is that prices will come down.”

Investors in July bought the fewest commercial properties since August 2006 and apartment building acquisitions were down 50% from June, data compiled by industry consultants at New York-based Real Capital Analytics Inc. show. Archstone-Smith Trust in August postponed its $13.5 billion sale to a group led by Tishman Speyer Properties LP until October. Mission West Properties Inc., the owner of commercial buildings in Silicon Valley, said on August 13 that the company’s $1.8 billion sale may fail after a bank withdrew funding.

“There are so many deals falling apart,” the chief executive officer of Lakewood, N.J.-based Lightstone Group, an owner of more than 20,000 apartments and 30 million square feet of office and retail space, David Lichtenstein, said. “People who can get out are getting out.”

About 930 commercial real estate transactions valued at $5 million or more closed in July, preliminary data from Real Capital show. That count could climb as much as 15% when all of the month’s deals are tallied, which would still be the lowest this year, the director of market analysis for Real Capital, Dan Fasulo, said.

Average prices for commercial properties might drop between 5% and 15% in the next two years depending on the type of property and its quality and location, an industry analyst at New York-based Morgan Stanley, the second-largest American securities firm by market value, Matthew Ostrower, said.

A senior analyst at Green Street Advisors Inc., a real estate research firm in Newport Beach, Calif., Michael Knott, estimates commercial prices may fall about 10% in the next 12 to 18 months and up to 15% in the office market during that period.

The Bloomberg Office Property Index fell 2.9%, led by SL Green Realty Corp., Manhattan’s largest office landlord. Commercial real estate brokers and managers declined. CB Richard Ellis Group Inc., the biggest commercial broker, dropped 9.3%. Jones Lang LaSalle Inc., the second-largest, fell 3.9%.

Commercial mortgage rates have climbed as defaults rose in the subprime part of the residential real estate market. About six months ago, a 30-year commercial loan with between 5 and 10 years of interest-only payments would have cost the borrower about 120 basis points more than the yield of the 10-year Treasury note. A similar loan would now cost between 160 and 200 basis points more than the 10-year Treasury’s yield of 4.6%, data compiled by New York-based Cushman & Wakefield Sonnenblick Goldman show.

The increase has halted a rally that lifted prices for office buildings, apartments, and hotels to records this year. The average price paid for high-quality office properties in city centers reached $291 a square foot, up from $188 in 2005 and almost double the average $152 in 2001, Real Capital reported.

Real estate investors typically purchase properties with the expectation that the yield will outstrip conventional investments and make their financing affordable.

When prices for prime urban office buildings fell in 2002, capitalization rates, or a property’s net operating income divided by the purchase price, rose to an average 9.25%, according to Chicago-based data provider Real Estate Research Corp.

That was almost 500 basis points more than the average rate of 10-year Treasury bonds at the time. Such yields attracted investors and by this year’s first quarter, the average cap rate had fallen to 6.5%.

New York-based Blackstone Group LP, manager of the world’s largest buyout fund, purchased Sam Zell’s Equity Office Properties Trust for $23 billion in February to gain about 540 office buildings in America. That worked out to a capitalization rate of about 5.3%, a record low for an acquisition of a real estate investment trust, according to Green Street Advisors. Including debt, the price was $39 billion.