In the spring of 1949, Sante Fe took delivery of 250 welded tank cars, class TK-N. Numbered 101100-101349, these cars were nearly identical to earlier TK-M cars, except the tanks and under-frames were welded instead of riveted. They had AB airbrakes and Ajax handbrakes. Trucks were 70 ton ASF A3 “Ride Control”. Running boards were diamond plate steel and dome platforms were open grid steel. When more diesel fuel cars were needed, General American delivered 200 more cars in mid-1953. Numbered in 98000-98199 series, these Class TK-O were identical to the TK-Ms. 

These tank cars served proudly and remained in service until the 1980s. Many were re-assigned to MOW serve and remained until the 1990s. In their later years, running boards were removed.