In order to study the effects of hydrostatic pressure on organic matter artificial maturation, pure Woodford kerogen was pyrolyzed under confined conditions at 300, 700, and 1300 bar. This technique allows to pressurize the kerogen and the generated effluents without any contact of inert gases or excess water. Gases, chloroform extract, and solid residues were analyzed. Results derived from the analysis of gases show no effects of pressure while the C-7+ hydrocarbons fractions is slightly affected. The amount of chloroform extract at the maximum of oil generation slightly decreases when pressure increases. Correspondingly, the Rock-Eval hydrogen index of the extracted solid residues increases. Pressure also slightly modifies the pyrolysis-gas chromatography fingerprints of the residual kerogen. Increasing pressure leads to the production of extracts depleted in saturates and shift the maximum of saturates generation to higher temperatures. The C-15+ n-alkane and aromatic gas chromatography traces do not show clear evidence of pressure effects. Spectroscopic investigation of the total extract gives detailed information on the aromatic substitution pattern : low pressures enhance the concentration of protonated aromatic carbons while high pressures favor the preservation of substituted aromatic carbons and increase the aromatic content of the polars. Gas chromatography and mass spectrometry data indicate that most of the hopane-maturation parameters are already at equilibrium in the temperature range investigated (280-400-degrees-C corresponding to the post-diagenesis zone) and no pressure effects are noticed. However, sterane fingerprints show variations related to pressure. Increasing effluents pressure induces a lower conversion of the kerogen and of the polars, and a higher thermal stability of some organic compounds, and favors aromatization reactions in the polars. The pressure effects observed are significantly lower than those observed by other authors. It is proposed that the nature of the pressurizing medium plays an important role in the hydrostatic pressure effect during organic matter maturation.