In the past, oilfield exploration was mainly a guessing process based on surface signs. The discovery of a field was followed by uncontrolled well drilling and oil lifting until the reservoir was eventually drained. Since then, tremendous changes and improvements in reservoir engineering have allowed the improved management of hydrocarbon reservoirs, removing the uncertainties across the entire range of exploration, development and production operations. The idea of using seismic waves - low-frequency sound waves - to map subsurface geologic structures gave birth to seismic technology. Acoustic pulses are propagated in sedimentary grounds or hydrocarbon reservoirs. Then the subsurface formations are mapped, based on the time it takes the sound waves to return to the surface after their reflection from various geological interfaces. Modern 3-D seismic technology is a vital tool for improved imaging of subsurface targets and reservoir characterization. It assists reservoir engineers not only in exploring and locating a reservoir but also in the full life cycle reserve monitoring, appraisal and decision-making. This is due to the fact that seismic data may provide appraisal-quality information on reservoir properties such as fluid flows, volumes, temperature and pressure. This improves early development decisions by reducing risk and uncertainty. Through better planning and increased hydrocarbon recovery rate by identifying bypassed reserves, the EU ATLASS project led to the development of tools and methods using four dimensional (4D) seismic data. The 4D seismic data is obtained through time-lapse 3D seismic surveys, which are repeated over time to monitor the reservoir characteristics throughout the productive life. The early assessment of reservoir properties can lead to the identification of potential geo-hazards and precise field delineation. This leads to justified decisions on facilities design, drilling strategies, location of bypassed zones, and finally, rational asset management. The techniques developed have been tested on real field cases demonstrating good results and have proven to be commercially viable.