South Sea share certificate. The South Sea Company, was a British joint-stock company founded in 1711 and granted a monopoly to trade with the islands in the "South Seas" and South America. Company stock rose greatly in value as it expanded its operations dealing in government debt, and peaked in 1720 before suddenly collapsing to little above its original flotation price; the notorious economic bubble thus created, which ruined thousands of investors, became known as the South Sea Bubble.