Upstream oil companies in the Middle East are more frequently confronted with decisions on continuing the oil production of mature oil fields. The low production rates of mature fields generate low revenues. Considerable investments are often needed to continue with the production of oil at a mature field until the field is depleted because the production stations installed are deteriorating. Oil companies are only willing to make considerable investments when future oil revenues compensate the investment. However recovering the investment is uncertain, because of the low and difficult to extract remaining oil volumes. Rationalisation projects are executed to assess if and how it is possible to continue with the production of oil at a mature field. As part of these projects, remnant life assessments are executed. The purpose of the assessment is to determine the condition of production equipment. The results are used to define effective concepts plans to prolong the remnant life of equipment and to support decision-makers in deciding if it is feasible to continue the production of oil at a mature oil field. However, remnant life predictions are inaccurate and the uncertainty of the remnant life prediction might result in economical suboptimal decisions. Uncertainties complicate decision-making processes, as decision-makers do not know to what extent they can rely on provided information to support them in decision making. The described problems result in the following research question. To what extent could uncertainty quantification of remnant life predictions of oil production assets have consequences for decision-making processes in rationalisation projects in the Middle Eastern oil industry? First a desk research was conducted that provided an overview of how decision-making processes under uncertainty can be arranged and what stakeholders are involved in the Middle Eastern oil industry. The results of the desk research were used as a basis for interviews with experts that are or have been involved in decision-making processes to analyse how decisions are actually made by Middle Eastern oil companies and what the role of remnant life assessments is in decision-making process of rationalisation projects. Finally an experiment has been conducted to determine if the uncertainty quantification of a remnant life prediction provides interesting results and how this could influence the decision-making process. The uncertainty of the remnant life prediction is caused by uncertainty about degradation mechanisms, the stability of the degradation rate and the production conditions in the past, present and future. Furthermore it is caused by assumptions that have to be made by the analysts to execute the analysis. The direct consequences for the decision-making process will be marginal. The only probable consequences are that the concepts plans that are designed and developed by project teams will be more detailed, feasible and effective and project teams will be able to time maintenance or equipment replacements better thanks to the quantified uncertainty of the remnant life prediction. Uncertainty quantification is not necessarily needed for decision-makers who prefer to use single value predictions in their decision-making processes and strategic behaviour by any of the stakeholder is considered to be improbable as it will harm the relation between stakeholders. Although the consequences for the decision-making are slightly disappointing in regard to the scope of this research, it is expected that uncertainty quantification will become more important in the future.