SAN ANTONIO – San Antonio’s office vacancy rate was 17.4 percent at the end of the third quarter, down 20 basis points from the second quarter, Grubb & Ellis reported. The market experienced 46,746 square feet of negative net absorption during the third quarter, lowering the year-to-date total of positive absorption to 112,636 square feet. Class A asking rental rates averaged $25.10 per square foot in the third quarter, a $1.18 decrease from the second quarter. Chevron Corporation’s recent acquisition and occupancy of a 150,000-sf building at 5200 Rogers Road reduced vacancy, Grubb & Ellis reported.