Abstarct: Reflection seismic is one of the most commonly used geophysical methods for the oil and gas exploration. The aim of this thesis is to provide a method for improvement of seismic reflection images in complex geological environments. In this thesis I show the application of the Common Reflection Surface (CRS) stack technique to improve the quality of reflection seismic images. Conventional seismic imaging method baxsed on the CMP stacking does not use the full potential of the dataset due to reflection point dispersal in the presence of dipping reflectors or laterally inhomogeneous media. Application of the CRS stack technique is advantageous in complex areas, since it involves information about the shape of seismic reflectors, i.e., dip and curvature, into processing. Moreover, a multi-parameter formula allows to sum up more traces during the stack. All together, this leads to better imaging results, especially to an improvement of the signal-to-noise (S/N) ratio. Reflection events in the CRS stack sections appear clearer and more continuous compared to conventional CMP stack sections. One of the problem of CRS method, is neglecting the conflicting dips problem in the section. It means that if two or more events conflict in a same point in the section, the CRS stack method could not handle this problem well. The conflicting dips problem is an important issue in the matter of imaging in complex structures. A modified version of the CRS stack, the common diffraction surface (CDS) stack, is a method that could solve the problem of conflicting dips that may happen frequently in complex and semi-complex structures. In this thesis, In two case studies I demonstrate the strength of the CRS stack technique applied to seismic reflection data of different quality. First, a seismic reflection data of semi-complex structure near some of the large gas reservoirs in Iran is processed by CMP stack, CRS stack and CDS stack methods. At first this data was processed by CMP stack method and its stacked section was obtained. The CMP-stacked section of this data shows an unconformity that separates horizontal event from dipping events. In that section, some of the events were not cleared for whatever reasons; therefore it was thought that it is needed to process the data with other methods like as CRS and CDS. In the CRS stacked section, it was observed that the reflection events were cleared better and also their continuity was more preserved. But due to the nature of CRS method, the problem of conflicting dips could not be solved. This problem could be solved, however, by common diffraction surface (CDS) stack method. Therefore, the CDS stack method is applied to the seismic data to solve some of the imaging problems in semi-complex structures. The CDS-stacked section imaged many reflection events missing in the CMP-stacked section. The problem of conflicting dips is also resolved in that section. The faults can be located and the reflection events at larger travel times are also well imaged. Finally, the CDS-stacked section shows that this method could resolve some of the ambiguities of imaging in semi-complex structures. Then, I perform the conventional CMP stack processing method on low-quality land data set of a mountainous area from the complex structure of the Zagros overthrust in south west of Iran. The CMP-stacked section contained a folding system and dipping laxyers, but both of them not well imaged in the section. Then, the common reflection surface stack method was applied to data. The folding and dipping laxyers in the CRS stack sections appear clearer and more continuous compared to conventional CMP stack sections. The other reflection and diffraction events at large travel times in some parts of the section were also imaged. Therefore, the CRS-stacked section showed that the common reflection surface stack could be used to partially solve some of the problems with complex structures.