Agriculture in southern Yemen is limited to the few areas with underground water for irrigation. Farmers grow three or four crops a year of barley, millet, sesame, sorghum, and wheat. Since the early 1980's, the Yemenis have worked to turn desert areas into farmland by means of dams, irrigation, and other water and agricultural development projects. Khat is the leading cash crop of Yemen. It comes from the leaves of a woody shrub that grows in the highlands.
Coffee is another important cash crop.
Coffee plants grow on terraces cut into the hills. Aden's oil refinery and port provide Yemen with much of its income. The oil refinery processes oil shipped from other countries, mostly those on the Persian Gulf. Ships of many nations use the port for refueling, repairs, and transferring cargoes. Until the early 1980's, Yemen had almost no other industry.