Hydrocarbons remain the most significant source of energy in the global map. Hydrocarbons and especially gas constitute a high priority, economical, environmental and geostrategic issue. Greece, participating in the TAP (Trans Adriatic Pipeline) project and beginning the exploitation of oil in the Aegean Sea, has a major role to play and a very demanding task to accomplish. Consequently, large emphasis is being given to the transportation of natural gas or petroleum by designing and engineering the best possible pipeline and pipeline corridor. The goal of this dissertation is to examine all the basic aspects and interdependencies of the overall designing and engineering process of subsea pipelines transporting hydrocarbons (in terms of efficiency, safety, cost and establishment of new technologies) and to propose optimal selections. Many essays and books have been written about subsea pipelines, examining engineering aspects individually. Consequently, the creation of a general methodology-engineering plan which not only analyzes the most important aspects of the designing process but also examines the interdependencies between the engineering stages, makes this dissertation a demanding task. In order to analyze these interdependencies and to present the methodology and structure of the dissertation, a subsea pipeline designing diagram for hydrocarbons transportation is initially introduced. Thereafter, the five thematic areas of the study are listed. In chapter 2, the optimal pipeline size and geometry is being examined. The subsequent chapters are dedicated to research of the following factors: the best possible material in chapter 3, the deposition or placement technique of the pipeline in chapter 4, the compressor or pump stations depending whether the transporting hydrocarbon material is gas or oil in chapter 5 and finally in chapter 6 the pipeline checking and maintenance. In almost every thematic area an example is being given in order to compare and examine the implementation of the optimal method-technology to the respective designing and engineering process.