Process for quantifying the pyritic sulfur in a sedimentary rock sample, in which at least the following steps are applied: A. said sample is heated in an inert atmosphere, between a first temperature of between 80°C and 320°C and a second temperature of between 600°C and 700°C, while following a first temperature sequence, and an amount of hydrocarbon-based compounds, an amount of CO and an amount of CO 2 released during said first temperature sequence are continuously measured; B. at least one portion of the effluents resulting from said heating of said sample in an inert atmosphere is continuously oxidized, an amount of SO 2 released by said oxidation of said effluents as a function of the time of said heating in an inert atmosphere is continuously measured, and at least one pyrolysis pyritic sulfur content S Pyrol Pyrit is determined from said amount of SO 2; C. the residue of said sample resulting from said heating in an inert atmosphere is heated in an oxidizing atmosphere between a third temperature of between 280°C and 320°C and a fourth temperature of greater than or equal to 800°C, while following a second temperature sequence, and an amount of CO and an amount of CO 2 released during said second temperature sequence are continuously measured; characterized in that at least one pyritic sulfur content S Pyrit contained in said sample is determined on the basis of a formula of the type: S Pyrit = S pyrol Pyrit ∗ 1 + β 1 − β + γ 1 − γ α wherein α is a parameter representing a proportion of said pyrolysis pyritic sulfur relative to said total sulfur, β is a parameter representing an effect of the mineral matrix on said proportion, and γ is a parameter representing an effect of the organic matrix on said proportion, the values of said parameters α and β being predetermined, and said parameter γ being determined from a formula of the type: γ = f OI HI wherein ƒ is a function of at least one oxygen index OI and of a hydrogen index HI, said hydrogen index HI being a function at least of said amount of hydrocarbon-based compounds measured during said heating in an inert atmosphere and said amounts of CO and of CO 2 measured during said first and second temperature sequences, and said oxygen index OI being a function at least of said amounts of CO and of CO 2 measured during said first and second temperature sequences, and in which said function ƒ is a linear combination of said oxygen index OI and of said hydrogen index HI which is expressed according to a formula of the type: γ = a ∗ OI + b ∗ HI + c, wherein a, b and c are predetermined constants. A. said sample is heated in an inert atmosphere, between a first temperature of between 80°C and 320°C and a second temperature of between 600°C and 700°C, while following a first temperature sequence, and an amount of hydrocarbon-based compounds, an amount of CO and an amount of CO 2 released during said first temperature sequence are continuously measured; B. at least one portion of the effluents resulting from said heating of said sample in an inert atmosphere is continuously oxidized, an amount of SO 2 released by said oxidation of said effluents as a function of the time of said heating in an inert atmosphere is continuously measured, and at least one pyrolysis pyritic sulfur content S Pyrol Pyrit is determined from said amount of SO 2; C. the residue of said sample resulting from said heating in an inert atmosphere is heated in an oxidizing atmosphere between a third temperature of between 280°C and 320°C and a fourth temperature of greater than or equal to 800°C, while following a second temperature sequence, and an amount of CO and an amount of CO 2 released during said second temperature sequence are continuously measured; characterized in that at least one pyritic sulfur content S Pyrit contained in said sample is determined on the basis of a formula of the type: S Pyrit = S pyrol Pyrit ∗ 1 + β 1 − β + γ 1 − γ α wherein α is a parameter representing a proportion of said pyrolysis pyritic sulfur relative to said total sulfur, β is a parameter representing an effect of the mineral matrix on said proportion, and γ is a parameter representing an effect of the organic matrix on said proportion, the values of said parameters α and β being predetermined, and said parameter γ being determined from a formula of the type: γ = f OI HI wherein ƒ is a function of at least one oxygen index OI and of a hydrogen index HI, said hydrogen index HI being a function at least of said amount of hydrocarbon-based compounds measured during said heating in an inert atmosphere and said amounts of CO and of CO 2 measured during said first and second temperature sequences, and said oxygen index OI being a function at least of said amounts of CO and of CO 2 measured during said first and second temperature sequences, and in which said function ƒ is a linear combination of said oxygen index OI and of said hydrogen index HI which is expressed according to a formula of the type: γ = a ∗ OI + b ∗ HI + c, wherein a, b and c are predetermined constants.