A rise in available space usually leads to a rise in vacancy unless demand outpaces this additional supply. The availability rate includes all available office space currently being marketed, which accounts for both occupied and vacant space. The vacancy rate accounts for only physically vacant space. Currently, the 25 largest blocks of occupied available space make up about half of the spread between the two metrics. The tenants in these blocks have committed to relocate, most are downsizing but some are expanding into larger facitlities.
Source: CBRE Research