Abstract Reservoir models are calibrated with production and pressure data to provide some confidence in the prediction of future reservoir production using the models. The last two decades have witnessed the proposal of numerous computer-assisted history matching techniques to ease the laborious task of reservoir model history matching and the related task of uncertainty analysis. Although many of these proposals have proved not to be viable when tried on real (i.e field) cases, some, such as experimental design, are now routinely used in the petroleum industry for history matching and uncertainty analysis. One notable, but largely under-utilised, technique that has generated a lot of interest for application to history matching is adjoint-based optimization. This paper discusses a field example of the application of the adjoint technique with experimental design to match the historical production and pressure data of a Niger Delta oil rim reservoir with a huge gas cap – the "SWX" reservoir in the "Beska" Field. The "SWX" reservoir, which is one of the few oil reservoirs in the gas-dominated "Beska" field, has been on production since 1992. A decision was to be made on the best time to commence gas cap blow down without jeopardising the life cycle hydrocarbon recovery from the reservoir. A properly history matched model of the reservoir was required for this decision. Adjoint technique was deployed to assist with the history matching of the "SWX" reservoir which had previously proved difficult to history match. The technique was applied both in the model-maturation stage for improved understanding of the reservoir and the final stages of the history matching exercise to fine tune the history matches of some difficult-to-match wells. The exercise provided an opportunity to test the merits and limitations of the adjoint technique. The result of these tests will be discussed in this paper.