Total oil production in Illinois, Indiana, Kentucky, and Tennessee in 1975 was 39 million bbl, down 5.3% from 1974. This compares with a decline of 8.9% in 1974 and of 11.9% in 1973. All 4 states had decreased production. Gas production in Kentucky in 1975 was 62.9 Bcf, a decline of 9.8% from 1974. Gas production in the other states is insignificant. A total of 2,445 oil and gas tests was drilled in 1975, up 24.5% from 1974 and 60.4% from 1973. Exploratory tests totaled 868, up 31.9% from 1974; of these 168 (19.4%) were successful.

Tennessee had 203 oil and gas tests in 1975, up 50.4% from 1974. Exploratory tests were up 68.2%. Most of the drilling was in Morgan, Fentress, and Scott Counties. Successful exploratory wells included 23 new fields, 8 new pools, and 13 extensions. None of the discoveries adds significant reserves. At Indian Creek field, operators began recycling gas to the Fort Payne reservoir for pressure maintenance, the first known secondary-recovery project in Tennessee. Oil and gas potential in fractured lower "Trenton" rocks in the Cumberland Plateau and eastward into the Valley and Ridge province was suggested by several wells in Grundy County that found gas in these rocks. Leasing activity continued in the Mississippian play in the northern Cumberland Plateau. Plans for deep tests in eastern ennessee appear to have been shelved because of tightened exploration budgets.

Illinois had 956 oil and gas tests in 1975, up 20.3% from 1974. Exploratory tests were up 14.9%, development wells 22.3%. Two oil fields, 6 successful newpool wildcats, 6 deeper pools, 8 shallower pools, and 12 extensions were discovered. None of the discoveries adds significantly to reserves. The two new fields are Louisville in Clay County and Vergennes in Jackson County. Production in Louisville is from the Aux Vases, McClosky, Salem, and Ullin (all Mississippian). Production in Vergennes is from the Devonian. Deep testing increased in Illinois. Of the 106 new-field wildcats drilled in 1975, 2 tested Pennsylvanian rocks, 31 Mississippian (all but 6 Valmeyeran), 59 Devonian-Silurian, 10 Ordovician (all "Trenton"), 1 Cambrian-Ordovician (Knox), 2 Cambrian, and 1 Precambrian. A Cambri n test in Johnson County was drilled to TD of 14,274 ft, a new depth record in Illinois. It was dry and abandoned, and Johnson County has no production.

Indiana had 374 oil and gas tests in 1975, down from 376 in 1974. Exploratory holes were down from 168 to 156. Development wells were up from 208 to 218. Success ratio of exploratory drilling was 12.8%. Successful exploratory wells included 3 new fields, 13 new-pool wildcat discoveries, and 5 extensions. One of the new fields, Elnora West, was an old dry hole that involved no new footage. A new-pool discovery, the Salem Limestone in Odon South field, established an additional productive reef-associated structure in Daviess County. In Owensville North Consolidated field, Gibson County, 12 wells were completed in the Salem in 1975. Drilling in 1976 is expected to continue at the current rate. Deeper stratigraphic units probably will command increased attention.

A total of 1,011 wells was drilled in Kentucky in 1975, up 45% from 1974. They included 315 exploratory wells (up 71.2%), 597 development wells (up 25.9%), and 99 miscellaneous wells. The success percentage for exploratory wells was 23.8% and development wells 58.8%. Successful exploratory tests included 17 new fields, 6 new-pool wildcats, 25 extensions, 11 shallower pool tests, and 16 deeper pool tests. Recent new discoveries in Lower Mississippian strata have caused many old wells to be deepened and many new tests to be drilled to the Fort Payne-Warsaw-Salem sequence in the Illinois basin part of Kentucky with much success. The discovery of Knox and shallower Ordovician production in Adair County has caused additional drilling and exploratory successes in adjoining Green County, and much more Knox prospecting throughout central Kentucky. Devonian shale-gas exploration will be curtailed severely in 1976 because of increased drilling costs. Several tests were drilled, the deepest of which was a 14,340-ft Precambrian test in Webster County.