Cased-Hole Pulsed Neutron Logging (CH PNL) measurements represent the standard solution for formation evaluation and time-lapse water/hydrocarbon saturation monitoring in cased wells. Today, this technology proves to be a valuable monitoring option also in the context of Carbon Capture, Utilization and Storage (CCUS) and Underground Hydrogen Storage (UHS) projects. In case of storage into depleted natural gas reservoirs, CH PNL tools can be used at the so-called spy wells to highlight plume arrival from the injector(s) and to possibly quantify its composition behind casing in terms of water, methane (CH4), carbon dioxide (CO2) and/or hydrogen (H2) relative saturations, according to the storage context (CCUS or UHS).