One of the most problematic issues facing aging assets and pipelines in the offshore UK oil and gas industry is exposure to increasing levels of H2S. Increasing levels of H2S can occur due to a number of factors. H2S can be generated within pipelines or topsides facilities due to poor microbial control, leading to SRB activity. This can affect the facilities and pipelines themselves, and anything downstream. H2S can also be generated by field souring, where SRB contamination of the reservoir has occurred due to poor microbial control of injection water. Finally, assets that have produced sweet gas over the majority of their lives may become gas deficient, requiring gas import for start up, gas lift and fuel gas purposes. Even though these assets have been exporting sweet gas, the only gas that may be available for import may be sour. In all of these cases, the existing infrastructure may have been constructed for sweet or slightly sour service, and may now face exposure to sour environments beyond the original design criteria, or beyond the materials limits defined by ISO 15156. In such circumstances, or where a new operator is taking over operatorship of older assets, a sour service assessment of the facilities and pipelines is strongly recommended. This publication describes the sour service assessment process. It also describes the justification criteria for continued operation where materials are found to be non compliant, and the remedial actions required where a suitable justification cannot be put in place. It will also discuss the generic findings from assessments performed on a number of assets and pipelines in the UK sector, and examine in detail the assessments performed for the TAQA Bratani assets and pipelines.