By the start of 20th Century, the tank car industry had produced 10,000 units. In-spite of growing competition, UTLX and its predecessor remained the largest tank car manufacturer of the period; its very close ties (subsidiary) to the Standard Oil Company had provided a very lucrative market. The relationship with Standard Oil was dissolved by court oder in 1912, enabling UTLX to expand its market base even further. During the 1930s Depression, UTLX's business strategy shifted heavily towards leasing tank cars to shippers and railroads.

Throughout World War II, the railroad tank car played a pivotal role in transporting critical aviation fuel and other oil products. More than half of UTLX's 40,000 tank cars were pressed into service on the nation's "Pipeline on Rails" which delivered one-million barrels of oil daily to Atlantic and Pacific terminals for overseas shipment. WWII also witnessed tank car builders increasingly employ a fusion-welding manufacturing process vesus the conventional riveting approach.