The Rock Eval method estimates the petroleum potential of rock samples by pyrolysis, according to a programmed temperature pattern. Released hydrocarbons are monitored by FID, generating two distinct peaks S1 (thermally distilled free hydrocarbons) and S2 (hydrocarbons generated from cracking of kerogen). The temperature at which the S2 peak is at a maximum is called Tmax, which gives an indication of kerogen maturity. Tmax can also be used to calculate vitrinite reflectance. In addition, carbon dioxide (CO2) released during pyrolysis can be monitored in real time by IR cell (S3), giving information on the oxidation state of the kerogen. Other diagnosic ratios can be calculated from the S1, S2 and S3 such as production index (PI), Hydrogen index (HI) and Oxygen index (OI).