Uniaxial strain experiments conducted on mudstone cores from overpressured horizons in Eugene Island Block 330 (Gulf of Mexico) reveal information about consolidation state, compaction behavior, and permeability. Maximum past effective stresses for two mudstone samples were experimentally derived and are within 200 psi of porosity-based estimates of in-situ stress. Laboratory measurements of stress ratio (K ₀ = 0.85) compare well with in-situ measurements made during leak-off and stress tests (K ₀ = 0.84 − 0.91). The high K ₀ values suggest that the sediment deformation is primarily plastic at in-situ levels of effective stress. A slope change on the stress-strain curve supports the observation of primarily plastic deformation following yield. Direct measurements of mudstone permeability at estimated in-situ levels of effective stress reveal layer-parallel and layer-perpendicular permeability of 5.32 × 10⁻⁴ md (5.25 × 10⁻¹⁹ m²) and 1.17 × 10⁻⁴ md (1.15 × 10⁻¹⁹ m²), respectively.