Oklahoma:

The new state became a focal point for the emerging oil industry, as discoveries of oil pools prompted towns to grow rapidly in population and wealth. Tulsa eventually became known as the "Oil Capital of the World" for most of the 20th century and oil investments fueled much of the state's early economy. In 1927, Oklahoman businessman Cyrus Avery, known as the "Father of Route 66", began the campaign to create U.S. Route 66. Using a stretch of highway from Amarillo, Texas to Tulsa, Oklahoma to form the original portion of Highway 66, Avery spearheaded the creation of the U.S. Highway 66 Association to oversee the planning of Route 66, based in his hometown of Tulsa.

Please answer a question about this article. If the question is unanswerable, say "unanswerable". What type of investments were important in early Oklahoma?
oil