major oilfield, east-central Algeria. The field lies in the Grand Erg (sand dunes) Oriental of the Sahara. The Hassi Messaoud oilfield, discovered in 1956, has a generally north-south axis, and the reservoirs are sandstones of the Paleozoic Era. In 1979 Hassi Messaoud's oil refinery was expanded, increasing its production capacity to about 9,500,000 barrels annually. In the early 1980s the field produced about half of the total Algerian oil output. Pipelines carry its oil to refineries in Algiers, Arzew, Bejaïa, and Skikda.