Production of marketable coal increased by 83 percent in the 1960-70 period to a level of about 29 million tons. The rise in output, however, was confined to lignite production, which grew more than fourfold during the decade. Production of bituminous and brown coal declined by 42 and 32 percent, respectively. Output of anthracite in 1970 equaled the output in 1960 but was 9 percent below the production level in 1966. Production of both anthracite and bituminous coal amounted to less than 400,000 tons in 1970. Strip mining has steadily grown in importance and accounted for 73 percent of the output in 1970. The Sixth Five-Year Plan (1971-75) calls for a rise in coal output to 33 million tons--an increase of about 13 percent. In the view of the minister of heavy industry, the planned increase is not large, but its attainment is difficult considering the character and condition of the mines. Experience has justified the minister's assessment. In the first two years of the five-year period, coal output rose by less than 1 percent. Crude Oil and Natural Gas Deposits of crude oil are located at Tyulenovo in the Dobrudzha region and at Dolni Dubnik, east of Pleven. Natural gas fields have been discovered near Vratsa and in the area of Lovech, south of Pleven. Reliable information on the magnitude of crude oil and natural gas reserves is not available. Statistics on current imports and official projections of import requirements, however, indicate that domestic production of oil and natural gas will continue to cover only a small fraction of needs. Production of crude oil rose from 200,000 tons in 1960 to 500,000 tons in 1967 but declined thereafter to 305,000 tons in 1971. Natural gas output, which had increased to 18.5 billion cubic feet in 1969, declined to 16.7 billion cubic feet in 1970 and 11.6 billion cubic feet in 1971. Imports of crude oil, mostly from the Soviet Union, increased almost 3-½ times between 1965 and 1971 to a level of 7.5 million tons. In 1972 the Soviet Union alone provided 95 percent of the country's requirements for crude oil and petroleum products. Imports of natural gas from the Soviet Union, through a pipeline still under construction, are scheduled to begin in 1974 at a level of 35 billion cubic feet and to continue at an annual rate of 106 billion cubic feet beginning in 1975. The planned 1975 import volume represents about three-fourths of the estimated requirements in that year.