Heinrich Ries, The New International Encyclopædia…
“ The rock in which the oil is found is spoken of as the reservoir, or oil-sand, and it is essential that this rock should be porous. The degree of porosity not only influences the quantity of oil which the rock can hold, but it may also influence the rate of flow of the well. Some wells may yield as little as 15 barrels per day; others may reach a production of 50,000 or 60,000 barrels per day. The porosity of the oil-bearing formation may also change from place to place and would account for the location of a profitable well at one point and a barren one a short distance from it. ”
