It is evident that accurate knowledge of the character and structure of the rock-formations in petroliferous territories is of the greatest importance in enabling the expert to select favourable sites for drilling operations; hence on well-conducted petroleumproperties it is now customary to note the character and thickness of the strata perforated by the drill, so that a complete section may be prepared from the recorded data.
Taking these figures as a basis, the total yield of oil from an acre of petroliferous territory would be a little over 5000 barrels of 42 U.S. gallons.
Some of the richest petroleum fields in Europe are spread in the region of the Carpathians, and are worked at Boryslaw and Schodnica near Drohobycz, Bobrka and Potok near Krosno, Sloboda-Rungurska near Kolomea, &c. Great quantities of ozocerite are also extracted in the petroliferous region of the Carpathians.