New estimates of anisotropy have revealed more details of the subsurface in Trinidad. These estimates are obtained by including more realistic constraints on the anisotropic inversion, which eventually helped boost the stability of the process. The anisotropic parameter , which, if not zero, implies the existence of anisotropy, is used to discriminate conservatively between shales and sands. The underlying theory is that shales induce anisotropy, positive in particular, and sands do not. The estimates, through have nice lateral correlation, react to the presence of faults. Correlation of these results with gamma-ray well-log measurements used as a shale estimate proves the credibility of the results. This finding confirms the hypothesis that anisotropy is caused by shales in the subsurface, and, consequently, we can use the inversion for interval to estimate lithology.