Oils and condensates with high concentrations of gasoline-range hydrocarbons typically lack adequate quantities of biomarkers used for thermal maturity and organic facies evaluations. I attempted a calibration of rock-based thermal maturity parameters between gasoline-range molecular parameters and nonmolecular maturity parameters such as Rock-Eval Tmax, vitrinite reflectance, and downhole temperatures. This enables maturity evaluation of volatile oils and condensates whose biomarker concentrations are at low or trace levels. The rock-based calibration data were used to assess thermal maturity of nonvolatile oils, volatile oils, and condensates from the Central Graben area of the UK North Sea and includes samples from high-pressure (gradients ) and high-temperature () hydrocarbon systems. Source rocks for theses North Sea oils and condensates are the Upper Jurassic Kimmeridge Clay and Heather shales, with a predominance of marine, algal type II organic matter.