This research aims to understand the mechanisms enhancing the fixation of low viscosity mineral oils, including tailings, in reactive inorganic matrices, by emulsification. To this purpose, significant amounts of a model low viscosity pure mineral oil (20%vol) are immobilized in alkali-activated materials (AAM), either based on metakaolin or blast furnace slag. In such case, Portland cement-based matrices are not adequate (emulsification delicate to manage and excessive setting retardation). Various surfactants are used to ease the oil emulsion. Visual observation and rheology evidence two distinct groups of surfactants. One contributes to structuring the oil/AAM fresh mix, with greater viscosity than without surfactant; the other includes non-structuring surfactants, without change in viscosity. Each group depends on the AAM considered. Whatever the AAM and the surfactant, the oil droplet size decreases significantly, without consistent correlation with the interfacial tension between oil/activating solution (AS). Interfacial tension alone does not explain the reduction in oil droplet size. Characterization of diluted ternary suspensions (solid particles – oil – AS) relates the structuring effect to interactions between oil and solid particles, through the surfactant polar head groups and non-polar hydrocarbon tails. A detailed mechanism explaining the oil stabilization and the mix structuring is discussed.