Distribution is Southern Sudan and western Ethiopia.
The smooth, shiny coat is dark brown, with the underparts bright white. Males darken with age, becoming a deep mahogany. The white-coloured facial markings include conspicuous eye rings, the insides of ears, and a throat bib. The outer sides of the legs have a vertical black stripe running down the length, while the insides are white in colour. The bushy tail is white underneath and terminates with a black tip. The "S"-shaped horns are found only in males, and bend sharply backwards, then curve up. They grow 40-69 cm / 16-28 inches long.
The kob is most active in the morning and late afternoon. Adult males are territorial, although the size of their defended ranges varies depending on the habitat and population density. The two extremes of this spectrum are a few relatively large areas, or a concentrated group of extremely small territories. These compact groups, called leks, are normally 200 meters / 640 feet in diameter, with 12-15 (rarely over 200) approximately circular individual territories which measure 15-30 m / 50-100 feet across. The resident male does not physically mark his area, rather he patrols its boundaries, often whistling loudly. The length of time a male may hold his territory varies from days to months. Population densities vary from 8-124 animals per square kilometer depending on the habitat. In southeastern Sudan, huge herds congregate along waterways during the dry season from November to April, at which point the density often exceeds 1,000 animals per square kilometer.