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"A reservoir in the geological sense is that portion of a sand-body or other rock in place, with pores of sufficient number and size as to be capable of holding and yielding a commercial quantity of oil or gas if they are present. It includes the whole porous volume whether it contains water, oil or gas." -Johnson, 1916

Reservoir

"A reservoir in the geological sense is that portion of a sand-body or other rock in place, with pores…