Early humans encountered naturally seeping oil deposits at scattered sites throughout the world. Spanish explorers of California in the 1540s noticed oil; likewise, the later De Soto expedition found it in what is today Texas.Yale chemist Benjamin Silliman Jr. earned the title, "father of the petroleum industry," thanks to his development of fractionation methods essential for deriving distillates from oil.Experiments with “rock oil” by Silliman in 1855 revealed that highly useful kerosene and other byproducts could be produced economically.In 1859, “Colonel” Edwin L. Cleveland and Pittsburgh became leading refinement centers.Kerosene became widely available as a fuel for heating and illumination. Discovery of cheap oil helped to change lifestyles throughout much of the world by enabling nighttime business and leisure activities.The oil era coincided with development of the steel industry. Such business luminaries as John D. Rockefeller expressed an early interest in the oil business, but he was negatively impressed by the chaos of the Pennsylvania oil fields. He understood that oil could fulfill its potential only if its production were stringently centralized—and he capitalized on the situation.The Pennsylvania oil heydey did not last long, but huge new discoveries were made in Louisiana, Texas, Oklahoma and California. They would dwarf the earlier supplies.