The trend for deep water flexible pipes, leading to high mechanical loads, requires using high strength steel grades which may present limitations in annulus environment. To address this issue, two R&D programs have been conducted: the first one consisted to calculate more realistic H2S content in the annulus considering its consumption by corrosion process. The second one consisted in using a polymeric layer which prevents H2S permeation from the bore to the annulus. Realistic case studies, representative of the different offshore development regions, originally designed using sour service steel grades with low mechanical resistance, have been optimized considering the H2S consumption by corrosion process in the annulus and the anti-H2S layer to allow the utilization of high strength sweet service steel grades, aiming at a cost reduction. Additionally, the utilization of technologies recently qualified or under development, such as new steel grades with improved mechanical resistance enabled for sour service applications using the two available solutions, is proposed to obtain a further optimization. Optimized designs are presented for each case study, along with the respective performances against the most relevant flexible pipe failure modes and cost impact. Furthermore, the maximum allowable H2S levels have also been assessed, extending the limits of each solution. By considering the H2S consumption by corrosion process in the annulus, the utilization of high strength sour service steel grades allows to decrease the cross section of the steel layers or the number of armour layers, leading to a weight reduction which is directly converted into cost saving. Regarding the anti-H2S layer, the complete elimination of H2S in the annulus makes possible the use of sweet service steel grades for sour fluid applications, being for extreme sour environments the only feasible solution. The precise assessment and control of H2S content in the flexible annulus, enable to deliver optimized designs for sour fluid applications with a significant impact on CAPEX and furthermore open frontiers for ultra-deep water even for extremely sour fluid applications.