America’s first giant oil field was the Trenton Field of Indiana; gas was discovered there in 1876 in Delaware County. Beginning in 1886 and continuing into the first decade of the twentieth century, gas and then oil were discovered and developed in east-central Indiana. A wild unregulated boom ensued that ultimately resulted in thousands of wells being drilled.
As gas and oil production declined in northern Indiana during the early 1900s, new discoveries were being made in the southwestern part of the state known as the Illinois Basin. Production reached a peak in 1956 at over 12 million barrels for the year, and has declined gradually since then. For a more detailed short history, see Oil and Gas in Indiana.