In 1921 San Antoni was served by 44 passenger trains every day. Twenty-two arrived and another 22 departed. The Southern Pacific station handled 10 incoming and 10 outgoing trains. The Missouri Pacific station took care of 8 incoming and eight outgoing passenger trains and the Missouri, Kansas & Texas station had four incoming and four outgoing trains. Most of these trains were locals that stopped at every depot along the way and others were fast "limited" expresses that only stopped at major cities. The most famous limited express trains were the Southern Pacific's "Sunset Limited," the Missouri Pacific's "Sunshine Special," and the Missouri, Kansas & Texas "Texas Limited."

In San Antonio, the Southern Pacific railroad station called Sunset Station served three different lines. All three had been independent railroads at one time. By 1921 they were divisions of the huge SP system. The largest and most significant of these was the Galveston, Harrisburg & San Antonio division which stretched all the way across Texas. It was part of the main SP line from New Orleans on the Gulf of Mexico in Louisiana to Los Angeles in California and the Pacific ocean. The Victoria Division had started out as the San Antonio & Gulf Shore. It started and ended in San Antonio, going south-east through La Vernia and Sutherland Springs to Victoria and the coastal region beyond, including Port Lavaca. By 1921 this was second class line with no express services and the two passenger trains in each direction stopped at every depot. By 1921 the third line, the San Antonio & Aransas Pass, was technically still independent but was in fact owned and controlled complete;y by the SP. Again this was a second class line, Another difference was the level of complexity. The line stretched to the Gulf of Mexico, principally Corpus Christi, but it had various junctions along the route with connections for trains to Houston, Aransas Pass and the Rio Grande valley. It also went north into the Hill Country, terminating in Kerrville.

In San Antonio, the Missouri Pacific railroad station served three different lines. All three had been independent railroads at one time. In 1921, all were still technically independent but each would be owned outright by MOPAC by the middle of the decade. The most significant line was the "International & Great Northern." This line stretched all the way from St. Louis, Missouri to Laredo at the Mexican border. As the line came south through Texas it split in Palestine to provide service to Houston. In the history of American railroading it is one of the most overlooked yet important lines ever created. The station in San Antonio also served what was in the 1920s, the most profitable short-line company in America. Originally known as the "Artesian Belt," it was renamed the "San Antonio Southern." Using the I&GN main line to exit San Antonio, trains switched at a place called Kirk southwards through Poteet and Jourdanton to a small community called Christine. The line was built by a land developer but just happened to go through fertile land for fruit crops, plus there was sand, coal and oil. The third company that used the MOPAC station in San Antonio was the "San Antonio, Uvalde & Gulf." This had started out as a line to serve communities south of Uvalde but it built eastward, crossing the I&GN main line at Gardendale. Corpus Christi investors took over the company to build a second direct line from the port city to San Antonio via Pleasanton where the renamed company was based. The SAU&G also used the I&GN main line to enter and exit San Antonio.

By 1921, the Missouri, Kansas & Texas railroad had its own station as well as tracks into San Antonio. The MK&T, often referred to as the Katy, had begun service to San Antonio in 1881, when it was part of the Missouri Pacific system. After the Katy became independent in 1891, it entered San Antonio using the tracks of the Southern Pacific and it used both the original SP depot and, after 1901, its replacement, Sunset Station. Also in 1901, the MK&T built its own tracks into San Antonio, allowing it to serve San Marcos and New Braunfels from its main hub in Texas, Smithville. The Katy also negotiated use of the Missouri Pacific line through Austin before it reverted to its own trackage to reach both Dallas and Fort Worth on its route to St. Louis. The Katy had no connections of its own from San Antonio other than its own line to the north but switching between both the SP to travel west and the Missouri Pacific to travel south was common. After the MK&T opened its own station in 1917, the terminal only served MK&T trains. At its peak, it served 8 trains a day, 4 incoming and four outgoing.