A simple and rapid automated Raman maturity method is calibrated using a suite of Carboniferous organic-rich mudstones and coals from the Inch of Ferryton-1 borehole in the Midland Valley of Scotland. Sediments in the borehole have been thermally matured by intrusion of a quartz dolerite sill, generating vitrinite reflectance (VR) values ranging from 0.5 to 6.0%VRo. Calibration curves are tested on eight other UK wells penetrating Carboniferous shales and coals in the Midland Valley and southern Pennine Basin. The G-band full-width at half maximum (G-FWHM) is the best Raman parameter to estimate the thermal maturity of organic matter (OM) in the oil and gas window (0.5 to 3%VRo) and has a very strong correlation with VRo.