The newest advances in seismic technology which now takes into consideration a 4th dimension; which is time. With 4-D seismic geologists are now able to monitor the movement and the mobility of oil as it is extracted in the production process. This is in fact three-dimensional (3D) seismic data acquired at different times over the same area to assess changes in a producing hydrocarbon reservoir with time. 4D is used when you shoot over an older 3D and compare the results and the changes to the reservoir. Changes may be observed in fluid location and saturation, pressure and temperature.