We have been in a seller's market for the last 6 years. A seller's market is a market with less than 6 months of inventory for sale. The San Antonio Board of Realtors® (SABOR) reports that May 2017 had 3.7 months of inventory. (May 2016 also reported 3.7 months of inventory.)
These numbers are the average, and I find that in some areas, and more specifically some neighborhoods, inventory is less than a month. The hottest areas in May are all in the northeast of San Antonio between Loop 410 and Loop 1604 east of US 281.