Exploratory drilling in the Eastern Interior basin continued in 1942 at about the same rate as in 1941 and resulted in the discovery of 54 new pools, all of which are small. In Illinois, the largest pools discovered in 1942 as measured in number of wells at the end of the year were the Covington pool, Wayne County, with 32 wells and a total yield to the end of 1942 of 1,070,000 barrels and the Bible Grove pool, Clay County, with 32 wells and a total yield of 55,000 barrels. The Markham City pool, Jefferson County, with 12 wells at the end of the year, had a total production during the year of 143,000 barrels.

The total number of completions, including both wildcat and pool wells, in the Eastern Interior basin was 2,518 (excluding gas input and salt water disposal wells) in 1942 as compared with 4,680 in 1941, a decline of nearly one-half. The reduction of drilling in pools was probably mainly the result of Federal Conservation Order M-68 issued December 23, 1941, which limited drilling to one well to 40 acres. A modification of this order was issued August 31, 1942, M-68-5, which permitted closer spacing for sandstone wells. With the wider well spacing there was a notable increase in the proportion of dry holes from 27 per cent in 1941 to 44 per cent in 1942.

Nearly all of the new pools discovered during 1942 produce from the Mississippian system, including both the Chester and Iowa series. A few of the new pools produce from the Pennsylvanian and Devonian systems and one, the St. Jacob pool, Madison County, Illinois, produces from the "Trenton" limestone of the Ordovician system. This caused a considerable revival of interest in the "Trenton" possibilities of western Illinois, but numerous tests resulted in no additional discoveries to March 1, 1943.

Production in the Eastern Interior basin in 1942 amounted to approximately 117,671,000 barrels which was a decline of 19 per cent from the figure of 145,534,000 barrels in 1941. (These totals include a small amount of production in northeastern Indiana and eastern Kentucky outside of the Eastern Interior basin.) These figures represent 8.5 per cent of the national total in 1942 as compared with 10.3 per cent in 1941.