The conversion of kerogen to petroleum is a thermally activated process. Many alternative forms of the rate equations have been proposed. Usually it is assumed that the present geothermal gradient has been unchanged in the past and the fractional conversion is determined. In this paper three limiting examples of time dependent thermal histories are considered: (1) a sedimentary basin is formed by thermal subsidence on initially hot lithosphere; (2) isothermal (cold) sediments are deposited instantaneously on crust with a constant (time independent) thermal gradient; and (3) a transient thermal event, i.e., a volcanic sill or dike, heats cool sediments. In each example, the conversion of kerogen to petroleum is determined and is compared with the steady state hypothesis. >

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