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Exploring for Oil and Gas Traps
Series Treatise in Petroleum Geology
Part Critical elements of the petroleum system
Chapter Evaluating source rocks
Author Carol A. Law
Link Web page
Store AAPG Store

Tmax is the temperature at which the maximum rate of hydrocarbon generation occurs in a kerogen sample during pyrolysis analysis. The S2 peak represents the rate of hydrocarbon generation (the area under the curve represents the amount). The temperature at the time the S2 peak is recorded during pyrolysis is Tmax, given in °C. Figure 1 shows output from a pyrolysis analysis and when Tmax is recorded.

Figure 1 Output from a pyrolysis analysis and when Tmax is recorded.

Interpreting Tmax

We can use the general guidelines for maturation levels given below for Rock-Eval pyrolysis Tmax for types II and III kerogens. Different pyrolysis techniques have different cutoffs for pyrolysis oil and gas generation zone boundaries. Pyrolysis Tmax can be significantly different for type I kerogen[1] or kerogen containing high sulfur concentration and is not a reliable indicator of maturity for these kerogen types.

Hydrocarbon generation zone Rock-eval pyrolysis Tmax, °c
Immature < 435
Oil (from type II kerogen) 435–455
Oil (from type III kerogen) 435–465
Gas (from type II kerogen) > 455
Gas (from type III kerogen) > 465

See also


  1. Tissot, B., P., Pelet, R., Ungerer, P., 1987, Thermal history of sedimentary basins, maturation indices, and kinetics of oil and gas generation: AAPG Bulletin, vol. 71, p. 1445–1466. Excellent review of the relationships between maturation indicators and hydrocarbon generation from kerogens.

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