What fossils are used in oil exploration?

In oil exploration, microfossils such as foraminifera, diatoms, and radiolarians are commonly used to identify potential oil reservoirs. These tiny organisms are found in sedimentary rocks and can indicate the age and environment of deposition, helping geologists locate oil-rich formations. Additionally, larger fossils like ammonites and trilobites can assist in correlating rock layers and understanding geological history. By studying these fossils, geologists can make more informed predictions about the presence of oil in subsurface formations.