Abstract The development of drilling technologies, the constant increase in the complexity of the geological conditions in the drilling areas, the need to involve hard-to-recover reserves in the development, and economic aspects have stimulated the development of horizontal drilling in the Russian Federation. Horizontal drilling volumes have increased several times over the past ten years. There are also changes in the design and completion of horizontal wells (multi-laterals for example), increasing the variety of geology of the target layers, the variability of the LWD. Therefore, taking into account the high volume of horizontal drilling in Rosneft, it is became necessary to systematize and classify wells by degree of complexity for geosteering in order to more effectively develop resources and improve the efficiency of geosteering of horizontal wells. This article will describe an approach to calculating the new parameter "Geosteering Difficulty Index" (GDI), which characterizes a horizontal well, and classify wells by geosteering complexity. Examples of optimization of used resources and services based on the presented classification are given, which, as a result, reduce costs and increase the economic efficiency of drilling horizontal wells. The drilling complexity index DDI (Drilling Difficulty Index) usually uses in international practice. The higher the DDI for a well, the more complex the design of the well, the more complex the technologies needed for drilling this well, the higher the qualification of personnel, etc. (Filimonov et al 2012). Similarly, we introduce a new industry indicator-the geosteering complexity index. It will take into account the geological features of the drilling area and may be used to rank wells by complexity for geosteering.