Gentlemen, you know that it can't be done."[2][3] In 1925, Applin co-authored a paper with Alva Ellisor and Hedwig Kniker,[2] which reported her findings that oil-bearing rock formations in the Gulf Coast region could in fact be dated using microfossils.[5] Applin remained with Rio Bravo until 1927, continuing to lead the use of micropaleontology in the oil industry.[4] Applin was able to have a successful career with the Rio Bravo Oil Company due to the fact her micropaleontology studies provided index fossils to the company which was vying for the best oil bearing stratigraphic layers.[1] The matching of micro index fossils between stratigraphic layers in not only the Gulf Coast region, but other regions as well, was the main form of oil exploration for oil companies.