In patients with fibrotic interstitial lung disease (ILD) who experience hypoxemia only on exertion, a portable oxygen concentrator did not increase physical activity in daily life compared with a device delivering room air. The study compared the two options in people with exercise-only hypoxemia due to fibrotic ILD. The use of portable oxygen did not have a positive effect on physical activity compared to the sham device. In the normoxemic group, there was a decrease in the walking distance of the 6MWD test when using a portable device. Portable oxygen significantly increased oxygen saturation (SpO2) during walking in both breathing conditions. Improvement of muscle oxygenation was confirmed only in patients with exertional hypoxemia (EID) in normal breathing conditions. Portable oxygen has a clinical effect in patients with severe ILD, but walking with a portable device delivering low oxygen flow did not significantly improve exercise capacity or subjective dyspnea.