By studing the fossils brought up from the drill pipe of a well the paleontologist can determine the age of the stratum being drilled through. The determination of the age is accomplished by correlating the fossils, either invertebrate or plant, including pollen (palenology), with those from other strata of known age. Thos allows the driller to reference where his bit is drilling in comparison with other nearby strata known to contain oil.Certain areas of the world known to have oil deposits usually have one thing in common, they most typically will derive their oil from a single stratum thus it is important to be able to identify it laterally as it moves vertically within the field.