This research studies the petrophysical properties and lithofacies of the Naricual Formation (Venezuela) through the nuclear-magnetic resonance measurements of 12 lithologically complex sandstone core plugs from well FGB-1. Bulk volume irreducible index, free fluid index, critical water saturation, and other properties were determined. NMR estimates of permeability were derived from T2 distributions using a modified Timur-Coates Free Fluid model. The results showed that the values of the novel FFI0.9/BVI ratio covered five ranges depending on the lithofacies of each rock in the Naricual Formation. Last, we conclude that NMR technology is an effective tool for the determination of rock facies.