The transmission expansion planning using high-voltage direct current (HVDC) projects requires representative data for reliability assessment based on international projects currently in operation. For that reason, this paper presents a comprehensive review of HVDC projects and contributes to the estimation of reliability parameters for both kind of HVDC technologies, namely: line-commutated converter (LCC-HVDC) and voltage source converter (VSC-HVDC). For each technology, the results of the reliability parameters of each of the main components forming the HVDC system, either LCC or VSC, are presented. In addition, these results are used for the calculation of the reliability of a bipolar HVDC system, showing its application and comparing the two technologies.