The main features of a methodology of a fire risk assessment for main pipelines for transportation of oil and gas are presented. The most important stages of a procedure of the fire risk assessment are the following: an analysis of a fire hazard (an identification of sources of hazards), a determination of frequencies of accidents with releases of oil and gas, a construction of accidents scenarios with an application of event trees and a calculation of the risk. The following factors influencing the frequencies of the releases of the products are analyzed: natural factors (kind of soils, hydrogeological, climatic, seismic factors), factors connected with a human activity near the pipelines, technological parameters (thickness of the tube walls, kind of materials of the tube walls, products pressure), corrosion, conditions of construction etc. The event tree method was used for the determination of the accidents scenarios. The following effects were used at the analysis: a jet flame in the case of an instantaneous ignition of the release, a flash fire and a vapor cloud explosion in the case of a delayed ignition of the release and a pool fire. Space distributions of impact factors for the mentioned above effects were determined, and conditional probabilities of fatalities were calculated using probit functions. Risk contours were then calculated, and an individual and a societal risk for a personnel and a population near the pipeline were determined for typical main pipelines for transportation of oil and gas.