Alloy specimens in the high-vanadium region of the vanadium-oxygen system were prepared by the reaction of high-purity vanadium foil and oxygen. The system was studied by x-ray and metallographic examination of quenched specimens, by differential thermal analysis, and by high-temperature x-ray. Solubility was determined as a function of temperature at equilibrium pressure. Equilibrium pressures were not measured. The solubility of oxygen in a-vanadium- -1.1 wt pct at 250 deg. C, 1.3 wt pct at 400 deg. C, 2.8 wt pct at 1,000 deg. C, and 3.5 wt pct at 1,200 deg. C--was found to be higher than previously reported. Retention of the high-temperature structure of a-vanadium by quenching is dependent upon the oxygen content and the quench rate. The a-phase cannot be retained above 2.1 wt pct oxygen even when water quenched from 1,000 deg. C. A peritectoid transformation was found at about 510 deg. C between 2.2 and 4.2 wt pct oxygen. The peritectoid phase, V9O (2.2.), has a composition range at 400 deg. C of 2.9 to 3.9 wt pct oxygen. A martensite structure results from water quenching a-vanadium alloys having oxygen contents from about 2.2 to 3 wt pct. The martensite transforms to the stable v9o upon reheating to temperatures in the range 200 deg.-250 Deg. C. B-vanadium has a composition range at 1,000 deg. C from 4.3 to slightly over 10 wt pct oxygen.