Pennsylvania-based Plymouth Oil Company was founded in 1923 by M. L. "Mike" Benedum (d. 1959). With operations headquarters in Sinton, the company profoundly affected the city's development by creating jobs, building company housing, and providing health and retirement benefits for many local workers. In 1933 Plymouth began leasing vast amounts of property in the area and in 1935 discovered oil on the Welder Ranch with completion of Welder Well C-1. In 1937 the company's second major discovery in San Patricio county was the Brigham Well No. 1 in the East White Point Field South of Taft.
In 1949 company executive W. M. "Mike" Griffith (d. 1954) organized the semi-professional Plymouth Oilers baseball team, providing a tremendous boost to the Sinton area. The company hired proven players as permanent employees and employed college athletes during the summers. The team's games at company-built Oiler Park were major community events. The team won state, national, and world semi-pro championships in 1951. The baseball team played until 1957, and the company operated until 1962, when it was purchased by Ohio Oil Company, later known as Marathon Oil.