A method is described for the analysis of oscillation measurements in critical assemblies where fissions are produced predominantly by thermal neutrons. The oscillation method developed in the CEA deals with the measurement of two signals: the “global” signal, which gives a representation of the sample reactivity, and the “local” signal, which gives the variation of the neutron density at the vicinity of the sample. Using a double calibration of the reactor by samples of enriched or depleted uranium and boronated uranium, it is possible to obtain independently the absorption and production reaction rates for plutonium in each sample, as a function of 235U reaction rates. The equivalent sample method is a more recent development and is based on the fact that a given perturbation of the absorption cross section, with any law of variation with energy in the thermal region, can be replaced by an absorption of well-known variation with energy which has the same effect on the neutronic density in the reactor beyond a small distance where spectrum effects are still appreciable. A series of measurements of uranium/plutonium rods performed in the CESAR reactor, from 20 to 400°C, is analyzed, and modifications of the absorption and fission cross sections of plutonium isotopes are proposed.