The source of cement in oilfields is critical to the prediction of the distribution of cements in the reservoirs and also prediction of reservoir quality. The source of mineral forming cements has been determined for the Storrington oolitic carbonate reservoir (Middle Jurassic Great Oolite Formation, Weald Basin, onshore UK) using a combination of petrography, electron microscopy, fluid inclusion analysis, atomic absorption spectrometry and stable isotopes analysis techniques. Petrographic interpretations revealed that ferroan calcite cement is the most significant diagenetic mineral and has a major control on reservoir quality. The preferred conclusion from this study is that the Great Oolite reservoir has acted as closed system during early diagenesis and has performed as open system during burial diagenesis. Also, elements for burial diagenetic cements have been sourced from neighbouring formation. Finally, stable isotopes analysis demonstrated that the dominant source of carbon in the Great Oolite reservoir is marine and is derived from the rock itself.