 The main aim of this project is to establish whether ambulatory oxygen in patients with fibrotic ILD whose oxygen saturation falls 88 on a 6MWT, leads to a significant improvement in health status. The core of the project will be a four week randomised, crossover controlled trial of ambulatory oxygen used during daily activities. The optimal Oxygen flow rate is determined by titration at screening visit and administered during activity for a two-week period, compared to two weeks off oxygen. 