<p>This study re-evaluates the petroleum system of the Sapphire Field, offshore Nile Delta, through integrated Rock–Eval pyrolysis, measured vitrinite reflectance (VR), and recalibrated 1D basin modeling. Pyrolysis data from 55 shale samples show total organic carbon (TOC) values ranging from 0.58 to 1.35 wt.%, indicating moderate organic richness. Kerogen typing reveals a predominance of Type III organic matter with subordinate Type II components, suggesting gas-prone characteristics. Despite locally elevated TOC values, corrected Tmax interpretation and newly tabulated VR data demonstrate that the Kafr El-Sheikh Formation is thermally immature. Consequently, it cannot be considered an effective thermogenic source rock, although limited biogenic gas potential may be present in shallow intervals. Reconstructed burial and thermal history modeling, calibrated to measured Tmax and VR data and constrained by realistic heat flow values, indicates that thermogenic maturity is attained only within the deeper Qantara Formation. This interval represents the principal viable source rock in the study area. Reservoir units include the Kafr El-Sheikh and El Wastani formations, while the Bilqas/Mit Ghamr formations provide effective regional seals. The revised petroleum system framework clarifies the timing of relationships in the Sapphire Field. All interpretations are now internally consistent with geochemical measurements, vitrinite reflectance data, and realistic thermal gradients, providing a robust basis for future gas exploration in the offshore Nile Delta and analogous deltaic settings.</p>