Exploratory drilling during 1951 led to the discovery of one small shallow-sand oil pool in southwestern Pennsylvania (Upper Devonian) and one small shallow-sand gas pool (also Upper Devonian) in north-central Pennsylvania. The total number of shallow wells drilled was 3 per cent less than in 1950. The Bradford field accounted for 80 per cent of Pennsylvania's oil production during 1951. The average daily oil production for the entire state in 1951 was 31,094 barrels, as compared with 32,488 barrels in 1950, a decrease of 4 per cent.

Eighty-four deep wells (Middle Devonian or deeper) were completed in 1951, as compared with 34 in 1950. Of these, 57 were gas wells and 27 were dry holes.

Major activities in Pennsylvania during 1951 were confined to the Oriskany sand gas territory of north-central Pennsylvania. The Leidy gas field in Clinton County, discovered early in 1950, underwent intensive development. It has now been extended for a distance of about 10 miles along the trend of the Wellsboro anticline, with maximum width of about 1¼ miles. The average rate of production of the field during 1951 was approximately 150,000,000 cubic feet of gas per day. Exploratory wells on five other prominent structures in north-central Pennsylvania were completed. One of these, an Oriskany test, was successful and will probably lead to the development of another Oriskany sand gas field. Two of the four unsuccessful wells were drilled through the Oriskany, one through the Albi n or Lower Silurian, and one represented a Cambro-Ordovician test on a well defined elongate dome in the closely folded Appalachians of southern Lycoming County.