The Messlah field, located in Arabian Gulf Oil Concessions 65 and 80 in the SE Sirte Basin, Libya, is a large combined structural-stratigraphic trap on the flank of the Messiah High. The basement rocks of the Messiah High are onlapped by the Lower Cretaceous Sarir Sandstone, where the pay is trapped The thickness of the Sarir Sandstone reservoir has been analysed using a statistical approach. Regression of the thickness of the Sarir Sandstone indicates that the unit wedges out against basement. The reservoir geometry developed as a result of syn-rift tilting of the Basement and truncation at the top of the Sarir Sandstone. Post-rift deformation of the Messiah field is restricted to subsidence with minor tilting, without significant faulting. The results of the linear regression are relevant to the exploration for similar traps in the area of the Messlah High.