Customs duties are important revenue earners and consist principally of import duties and tonnage dues; the former are levied on dutiable commodities, the latter on ships that call at Taiwan ports. The average rate was 8.2% in 2002. Duties range from 2% to 60%. The seven duty categories include rubber tires, cement, beverages, oil and gas, electrical appliances, glass, and automobiles. In 1998, Taiwan reduced tariffs on a wide range of items. Articles imported for military use, for relief, or for educational or research purposes are exempted from import duty. Duties on imported raw materials for business can be rebated. Some agricultural products are prohibited from importation, such as rice, sugar, chicken, some pork cuts, peanuts, and certain dairy products. Imports from Japan and mainland China are restricted due to balance of payments problems.