The U.S. office vacancy rate fell to 16.0 percent in the second quarter, the lowest in seven years, research firm Reis Inc said on Monday. The rate declined by 10 basis points from the first quarter and marked the eighth consecutive quarter of decrease in the national vacancy rate. Overall net absorption increased by 5.4 million square feet of office space in the second quarter, a significant decline from an increase of about 11.6 million square feet in the preceding quarter, Reis said.