The anisotropy parameter δ can provide useful information about the type of fluid in fractured rock: that is, to distinguish gas from water in fractures. We analyze the anisotropy parameter δ in the gas-saturated HTI model of fractured rock, as well as in the water-saturated one, using specific numerical modelling based on the velocity data from ultrasonic experiment. That is, we construct transversely isotropic (HTI) mathematical model “Linear-Slip”, which contains the same network of vertical aligned fractures as in the physical modelling of fractured rock. We first calculate the fractures’ weaknesses ΔN and ΔT, and then use them to recover the HTI stiffness tensor. We first derive analytical formula for the anisotropy parameter δ for the gas-saturated model. In the water-saturated model, the normal fracture weakness ΔN should be zero. So, taking this fact into account, we derive a formula for δ of the water-saturated model. We compute the corresponded δ-parameters for five HTI-models (which differ only in their fracture concentrations) for the gas-saturated case and the water-saturated one. It turned out that the parameter δ in gas-saturated rocks is greater than in water-saturated rocks (on average 15% more in absolute value). Therefore, the anisotropy parameter δ can serve as an indicator for distinguishing gas from water in fractures. In wide-azimuth 3D/2D seismic data, we can obtain the δ-parameter from azimuthal NMO-velocity analysis (NMOA). And then, knowing δ, we can apply AVOA analysis to check the obtained δ, as well as estimate the concentration of fractures and their azimuthal direction. Thus, by using integrated NMOA + AVOA analysis, we can obtain valuable information for the characterization of fractured reservoirs.