Thermal neutron capture γ-ray spectra for 16,17,18 16,17,18 O(n,γ) reactions were measured. Absolute transition probabilities were determined for each reaction by a least-squares fit of the γ-ray intensities to the decay schemes after accounting for the contribution from internal conversion. The transition probability for the 870.76 keV γ-ray from 16 O(n,γ) was measured as Pγ (871)=96.6±0.5% and the thermal neutron cross section for this γ-ray was determined as 0.164±0.003 mb by internal standardization with multiple targets containing oxygen and stoichiometric quantities of hydrogen, nitrogen, and carbon whose γ-ray cross sections were previously standardized. The γ-ray cross sections for the 17,18 O(n,γ) and 2 H(n,γ) reactions were then determined relative to 870.76-keV γ-ray cross section after accounting for the isotopic abundances in the targets. We determined the following total radiative thermal neutron cross sections for each isotope from the γ-ray cross sections and transition probabilities; σ0(

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