Three experiments were conducted to estimate the bioavailability of cobalt (Co) in reagent grade and feed grade Co sources for sheep. In Experiments 1 and 2, 27 mature sheep were assigned randomly to nine treatment groups. Treatments were the basal diet supplemented with 0, 20, 40, or 60 ppm reagent grade (RG) Co sulfate (standard) or 40 ppm Co as either RG Co oxide or Co carbonate or feed grade (FG) Co oxide, Co carbonate, or a Co oxide by-product (BP). Sheep were fed the experimental diets for 20 days. In Experiment 1, liver, kidney, heart, muscle, and spleen were collected. In Experiment 2, liver, kidney, and serum were collected. In Experiment 3, lambs were fed the basal control diet or basal supplemented with 0, 20, 40, or 60 ppm Co as RG Co sulfate or FG Co glucoheptonate for 16 days and liver, kidney, and serum were collected. Vitamin B 12 was determined in serum and liver in Experiment 3. Cobalt concentration was determined on all other samples. There was no effect of Co treatment on feed intake in any of the experiments. Tissue Co concentrations increased with Co supplementation in all three trials. In Experiment 1, serum and liver vitamin B 12 concentrations increased with increasing Co up to 40 ppm added Co. In Experiment 3, vitamin B 12 concentrations were variable but generally decreased with increasing Co as did total corrinoid concentrations. Based on liver and kidney Co concentrations the Co in Co sulfate, both carbonates and the glucoheptonate was more available than that in any of the three oxide forms.