It has long been noticed that in his Oedipus, Seneca diverges conspicuously from his primary model, Sophocles’ Oedipus Tyrannus (OT), in a number of aspects. Prominent among these is an expansive, two-part ritual sequence at the play's center, comprising a prodigy-filled yet spectacularly unsuccessful sacrifice and extispicium followed by a more successful, if no less terrifying, necromancy to raise the slain Laius. This article concentrates on the sacrifice and extispicium (Sen. Oed. 288-402). I argue that in this episode Seneca has employed tragic contaminatio (the weaving into one play of significant elements from two or more different source plays) and allusion to produce an exceptionally innovative scene that is a remarkable display of the Roman playwright's ingenuity. For while Sophocles’ OT remains an active intertext, Seneca has also imported elements from Euripides’ Phoenissae. His primary model for the passage, moreover, is actually to be found in a different Sophoclean Theban play, Antigone. Specifically, Seneca has reworked and elaborated upon the climactic reversal scene between Creon and Tiresias in Antigone (998-1114), in which the seer reports on the corruption of the prophetic rites he has just performed and identifies Creon as the cause of the pollution, both for his continued refusal to allow the burial of the fallen Polyneices and for his entombment of the living Antigone.