Output from Spindletop peaked at around just after it was discovered and then started to decline. Later discoveries made 1927 the peak year of Spindletop production, but Spindletop's early decline forced Gulf to seek alternative sources of supply to sustain its substantial investment in refining capacity. This was achieved by constructing the 400-mile (640-km) Glenn Pool pipeline connecting oilfields in Oklahoma with Gulf's refinery at Port Arthur. The pipeline opened in September 1907. Gulf later built a network of pipelines and refineries in the eastern and southern United States, requiring heavy capital investment. Thus, Gulf Oil provided Mellon Bank with a secure vehicle for investing in the oil sector.