Development of phosphorescent oxygen sensing materials based on commercially available semicrystalline polymer fibres (polyolefins, PP and PE) is described. The Pt-benzoporphyrin dye was incorporated into the nanoporous network of polyolefin fibres formed upon tensile drawing in the presence of physically active liquid environment via the mechanism of solvent crazing. Optimised fibre sensors showed optimal sensitivity to O2, stable calibration in the range of 0–21 kPa O2, reversible operation, linear temperature dependence and no significant cross-sensitivity towards humidity. The high surface area to volume ratio of the solvent-crazed polymer fibres enabled relatively bright phosphorescence intensity signals and fast response. Widefield and confocal microscopy combined with lifetime imaging were used to investigate the fine structure, dye distribution and heterogeneity of quenching by O2 in the solvent-crazed dye-containing polymer fibres.