Resin evaluation using pulsed neutron tool. At least some of the example embodiments are methods including: interrogating an area behind a casing material within a borehole with a plurality of neutrons; obtaining a count rate of inelastic gammas of a first gamma detector for a particular borehole depth, wherein the inelastic gammas comprise gammas emitted in inelastic collisions of the plurality of neutrons with matter behind the casing material; determining an inelastic carbon-oxygen ratio from the inelastic count rate of the first gamma detector; and determining an indication of the composition of the matter behind the casing material from the inelastic carbon-oxygen ratio from the inelastic count rate of the first gamma detector.