This paper considers the dispersion of gas releases within congested semi-confined volumes, such as offshore process installations. The individual phenomena that influence the dispersion, namely the background ventilation rate, the rate of release of gas, the near-field jet behaviour and the interaction of jets with solid surfaces such as walls, are considered separately. Topics requiring more work are identified. The composite problem of dispersion in a semi-confined obstructed volume is then addressed. A range of approaches are discussed and examples are given of calculations made using one approach. These highlight some of the more important features which control the dispersion of gas. The paper ends with a discussion indicating the need for more experimental data at a larger scale.