Vitrinite reflectance of the Upper Devonian–Carboniferous succession in the Kinsale Harbour–Old Head of Kinsale area ranges from 4.06–5.21% (m) and 6.21–7.82% (max) which is indicative of meta-anthracite coal rank. No correlation is apparent between vitrinite reflectance and stratigraphic position through c. 2 km of section, suggesting that near-maximum temperatures were maintained until after Variscan folding. Low reflectance values of 0.62% and 0.30–0.35% (m) at the local base of the Jurassic succession in the North Celtic Sea Basin (Well 48/30-1) and onshore at Cloyne respectively, indicate a major discontinuity in the maturation profile in the region. Comparison with high reflectance gradients from Upper Palaeozoic successions in the Halen and Turnhout boreholes in Belgium and the Münsterland No. 1 borehole in West Germany suggests that a thick (5–7 km) cover of pre-Permo-Tnassic rocks must once have been present in the Munster Basin to account for the high maturation levels observed. Whether the cover was emplaced by Silesian sedimentation or by late Palaeozoic thrusting is unclear.