Vacant office space in the U.S. office market rose to 13 percent during the first quarter, according to CBRE, the international real estate services firm.

But Wilmington was one of the cities that reported the largest quarterly declines in vacancies. Wilmington's vacancies dropped by 1.2 percent.

Other cities reporting large quarterly declines in vacancies were Kansas City, Tulsa and Las Vegas.

The vacancy rate in suburban markets increased to 14.2 percent. Downtown vacancy rates increased to 10.7 percent.

"The office market appears to have reached equilibrium and the strong economy, including solid employment numbers, is likely to help offset rising supply," said Jeffrey Havsy, CBRE's chief economist.