To precisely identify the location of oil and gas, a type of sampling known as mud logging is performed during drilling. When carefully analyzed, the mud that serves as the drill bit's lubricant and coolant tells a precise story about downhole conditions, including the amount of oil and gas present at various locations. Other forms of measurements include:

  ·electric logging, which measures characteristics of rock around the well bore
 
  ·caliper readings, which measure the diameter of the well bore
 
  ·electrical resistivity readings, which identify fluids
 
  ·and gamma ray measurements, which reveal gas