Paleoclimate records of geologic time periods characterized by extreme global warmth such as the mid-Cretaceous are important for a better understanding of the Earth's climate system operating in an exceptionally warm mode. Here we applied an organic geochemical proxy (TEX86) on organic matter–rich Albian–Santonian sediments, recovered from Ocean Drilling Program Leg 207 Sites 1258 and 1259 on Demerara Rise, to reconstruct sea surface temperatures (SSTs) in the western equatorial Atlantic. Preceded by a stepwise Cenomanian warming trend (∼31–35 °C), the onset of the Cretaceous thermal maximum coincided here with the Cenomanian-Turonian boundary event. Once established, this extreme warm climate regime, characterized by averaged tropical SSTs close to 35 °C, lasted up to the Turonian-Coniacian transition. Two pronounced cooler intervals (∼2–3 °C) interrupt this otherwise remarkably stable record, providing the first δ18O independent evidence for middle Turonian cooling that previously has been attributed to glacioeustatic sea-level lowering. Coniacian SSTs decline stepwise, reaching a minimum in the Santonian (∼32–33 °C), where cooling is most pronounced, presumably concomitant with the first progressive opening of a deep-water passage through the equatorial Atlantic gateway.