Downdip versus updip gas injection options have been evaluated for a deepwater multi-reservoir development discovered and appraised over the last few years. At the time of the study, the development plan called for gas injection in the Alpha field until gas export to the mainland became available. The name of the field has been changed to preserve confidential data. The depositional model of the Alpha field envisages stacked turbiditic channel systems meandering from east to west. The field is tilted approximately 30 degrees north-south due to post-deposition tectonic movement. As a result, the apex region of each meandering channel may form attic-traps that can only be swept by a fluid lighter than oil. Whilst downdip gas injection offers the potential of recovering the oil in these attics, it also carries the risk of gas over-running towards updip producers causing excessive gas production. A study was performed to assess various gas injection scenarios using 2D and 3D reservoir simulation. A simple model utilising a single channel at various dip angles was built prior to any detailed simulation to study fluid movements and demonstrate proof of concept. Fully integrated geological sector and full-field models were then constructed using an object-based modelling technique to assess downdip and updip gas injection options in multiple equiprobable stochastic realisations. The study concluded that counter to conventional thinking, downdip gas injection both delays gas breakthrough and recovers more oil in this reservoir. These benefits were the result of: Downdip injection scenarios offering greater opportunities for gas solution in the highly undersaturated oil prior to accumulation at the crest;Increased offset between producer and injector.Displacement of trapped oil in tilted-channel attics improving sweep; Based on the outcome of this study, downdip gas injection was integrated into the development plan. Later developments in the project enabled gas export from first oil, rendering gas injection unnecessary.