Vitrinite reflectance values (%R_o) calculated from commonly used methods are compared with respect to time invariant temperatures and constant heating rates. Two monofunctional methods, one involving a time-temperature index to vitrinite reflectance correlation (TTI-%R_o) and the other involving a log(%R_o) to depth correlation, yield vitrinite reflectance values that are similar to those calculated by recently published Arrhenius-based methods, such as EASY%R_o. The approximate agreement between these methods supports the perception that the EASY%R_o algorithm is the most accurate method for the prediction of vitrinite reflectances throughout the range of organic maturity normally encountered. However, calibration of the e methods against vitrinite reflectance data from two basin sequences with well-documented geologic histories indicates that, although the EASY%R_o method has wide applicability, it slightly overestimates vitrinite reflectances in strata of low to medium maturity up to a %R_o value of 0.9%. The two monofunctional methods may be more accurate for prediction of vitrinite reflectances in similar sequences of low maturity.

An older, but previously widely accepted TTI-%R_o correlation consistently overestimates vitrinite reflectances with respect to other methods. Underestimation of paleogeothermal gradients in the original calibration of time-temperature history to vitrinite reflectance may have introduced a systematic bias to the TTI-%R_o correlation used in this method. Also, incorporation of TAI (thermal alteration index) data and its conversion to %R_o-equivalent values may have introduced inaccuracies.