Ten-X is not particularly optimistic about the outlook for the U.S. office market, but it is more sanguine about certain markets, including Portland.

The company said Portland is among the top five markets, including Dallas, Long Island, Sacramento and Tampa, in which investors should consider buying office properties. These markets have either strong overall economies and specific sectors creating jobs, or constricted office supply.

In Portland's case, the city is attracting enough newcomers to spur population growth of 1.7% in 2017, a rate that has accelerated for a third straight year and is more than double the U.S. average, the report said. On the other hand, while Portland's economy continues its expansion, information jobs are declining and the city is not generating robust office job growth.

Demand for office space in Portland is strong enough to absorb new supply. Vacancies fell below 12% for the first time in the cycle, according to Reis data, and rents are at an all-time high.

"Ten-X expects reduced availability to drive rent growth in the mid-3% range through 2018, pushing [net operating income] above 4%," the report said.

By contrast, Ten-X said Houston, San Francisco, Memphis, Baltimore and Suburban Maryland are the top markets where conditions might cause investors to consider selling their office properties.

"These markets have either seen tepid office job growth this cycle contribute to high vacancy rates, or have had strong economic recoveries lead to larger new office supply than the market can digest," the report said.