In 1991, the United States consumed about 21 mt (23 million st) of gypsum. Of that, about 70 pct was produced domestically and 30 pct was imported. About 15 mt (17 million st) was calcined and consumed as plaster or wallboard and 5 mt (6 million st) was used in uncalcined form as a cement-setting retarder or as a soil conditioner. At least 80 countries are known to produce gypsum. Estimated world production in 1991 was about 98 mt (108 million st), about the same as in 1990. The United States is the largest producer and consumer of gypsum. Canada is the second largest producer and exports a significant part of its production to the United States.