Rock fracability characterization is a key issue for stimulation of unconventional reservoirs. This property controls hydraulic fracture initiation, propagation pressure and Stimulated Reservoir Volume (SRV), which in turn control well productivity. Brittleness and its opposite, toughness, are terms used to describe rock fracability. This paper discusses the use of a linear elastic fracture mechanics approach based on the critical stress intensity factor (KI) to characterize rock fracability.This article presents results of experimental studies using real Vaca Muerta Formation shale from outcrop samples. Fracture Toughness (KIC) is determined using notched 1.5“ plugs machined from rocks, which can be re-used several times and require much less material than standard Brazilian discs and semicircular three point bending specimens. A novel experimental set up has been used, in which KI is applied by means of a hydraulic system. This allows the analysis of the influence of the fluid composition. The influence of chemical and mineralogical rock composition, saturation levels and exposure conditions (different fluids) upon fracability is discussed in terms of KIC measurements conducted on rock samples.The use of different fluids as saturation media in controlled laboratory conditions has shown a decrease in the KIC values of rock samples. Advantages and limitations of the experimental conditions are discussed as well as the influence of different mechanism of fracture toughness variation on rock samples with fluid content.