The article summarises results of quantitative risk assessment for the operation of six large gasholders in the area of great industrial agglomeration in the Czech Republic. Gasholders for storing combustion gases contain significant amounts of dangerous substances, especially of carbon monoxide and hydrogen. That is why safety reports on these gasholders were prepared in the framework of implementation of the SEVESO 11 Directive. Although gasholders have gradually been shut down in the world, they still bring the heavy industry in the area of the city of Ostrava a considerable financial saving. Chosen industrial plants actually combust cheap waste gases, i.e. coking, converter and blast-furnace gases instead of natural gas. As a consequence, the gasholders are not expected to be closed in the near future either. With regard to the age (the oldest gasholder is more than 60 years old) and a high population density in the area concerned, it was necessary to do a detailed risk analysis. Many methods, from simple screening and indexing methods (Selection Method from Purple Book CPR 18E. IAEA-TECDOC-727 method, method based on the Dow's Fire and Explosion Index), through the systematic HAZOP method, modelling of the dispersion of toxic gas releases up to the determination of risk probability and societal acceptability were employed for the assessment of risks of the gasholders. The goal of the article is to present results of the assessment of risks connected with the operation of the large gasholders, to furnish information about possible operational problems and to verify the applicability of recognised methods of risk analysis for these specific serious sources of risks. (C) 2004 Elsevier Ltd. All rights reserved.