The Norwegian Oil Industry Association (OLF) and Federation of Norwegian Manufacturing Industries (TBL). Rev. 4, Nov. 2001. 10p. This NORSOK standard, rev. 4, is therefore completely rewritten to fully align with the new ISO standard and now only includes the requirements and guidelines considered necessary to add to the ISO standard for the broad needs of the Norwegian petroleum industry. This NORSOK standard must therefore be read together with ISO 15138.