Ukraine is one of the world's most important mineral producing countries, in terms of both the range and size of its reserves. There are nearly 8,000 separate deposits, harboring some 90 different minerals, of which about 20 are economically significant. About half of all the known deposits are under exploitation. Coal reserves in Ukraine amount to 47.1 billion tons. The annual domestic demand for coal as fuel is about 100 million tons, of which 85 percent can be satisfied by domestic production. Ukraine has oil and gas fields that meet 10 percent of her oil and 20 percent of her gas consumption, respectively. Ukraine contains natural gas reserves of 39.6 trillion cubic feet, but only about 20 percent of the country's demand is met by domestic production. Deposits of iron ore (estimated at 28 billion tons), manganese ore (3 billion tons), chalk and limestone (1.5 billion tons) are also large in Ukraine. The domestic industrial sector suffers from constant energy shortages and energy supply payment debts totaling about $792 million at the end of 1995.