Cos d'Estournel is a vineyard and winery in the Saint-Estèphe appellation of the Médoc. In the 1855 Classification, it was classified as a second growth and remains one of the most prominent and sought-after of all Bordeaux wines. Historically, the Cabernet Sauvignon-dominant grand vin has had a high percentage of Merlot compared with other Médoc growths, although this has lessened in recent years. Cos d'Estournel is dark, brooding and tannic when young, developing complexity and intensity with time.
The estate is situated in the very south of Saint-Estèphe, just north of Pauillac's Lafite Rothschild. The south-facing vineyard slopes gently down to the Jalle du Breuil stream which separates it from Lafite. In old Gascon, "cos" means "hill of pebbles", and the vineyard does consist of deep Quaternary gravels and clay on limestone bedrock. It covers 91 hectares (225 acres) and is planted 60 percent to Cabernet Sauvignon and the rest Merlot.