Monahans is a city in and the county seat of Ward County, Texas, United States. A very small portion of the city extends into Winkler County. The population was 6,821 at the 2000 census.Monahans is the home of the Million Barrel Oil Tank. Shell Oil Co. constructed the tank in 1928 to hold crude oil waiting to be shipped. However, because of leakage and evaporation, the tank was not effective and was dismantled during the 1930s. Located in a region where native Comanches, Mescalero, and Lipan Apache Indians once roamed, Monahans' history as a community extends back to the late 1880s with the expansion of the Texas and Pacific Railway across the south plains.