The influence of water vapour and additives on the decrease in surface area of gamma Al₂O₃ at 1378 K, before its transformation into alpha Al₂O₃, was investigated. The experimental rate of this decrease was found to vary as P _H2O at constant value of surface area and for a value of water vapour pressure ranging from 0.1 to 1 kPa. This reduction in surface area was inhibited by a slight addition of Mg²⁺, Ca²⁺, La³⁺, Th⁴⁺ or Zr⁴⁺ ions but its rate was drastically increased by increasing both additive content up to 4% (cationic fraction) and oxygen pressure. The influence of water vapour can be explained quantitatively using a mechanistic model for initial sintering of oxide powders. This model is based on a description of material transport by means of structural elements of alumina, point defects, and their chemical interaction with the calcination atmosphere.