UP 844: a 4-8-4 Northern type express passenger steam locomotive (class FEF-3), operated in excursion service since 1960. It was the last steam locomotive built for UP and has been in continuous service since its 1944 delivery. Many people know the engine as the No. 8444, since an extra '4' was added to its number in 1962 to distinguish it from a diesel numbered in the 800 series. It regained its rightful number in June 1989, after the diesel was retired and donated to the Nevada Southern Railroad Museum in Boulder City, Nevada. A mechanical failure occurred on June 24, 1999, in which the boiler tubes from the 1996 overhaul, being made of the wrong material, collapsed inside the boiler and put the steam locomotive out of commission. The UP steam crew repaired it and returned it to service on November 10, 2004. It was rebuilt again in 2015 and returned to service in 2016. In addition to being one of UP's oldest locomotives, it is the only steam locomotive to never be officially retired from a North American Class I railroad.^[1]UP 4014: a 4-8-8-4 Big Boy class freight steam locomotive, began operating in excursion service in 2019. It is largest operational steam locomotive in the world. Delivered in 1941, the locomotive operated in revenue service until it made its last run on July 21, 1959, and was placed in storage until it was officially retired in 1961. Following retirement, it was donated in late 1961 to the Rail Giants Train Museum in Pomona, California, where it became one of the eight Big Boys preserved around the United States. On July 23, 2013, it was announced that the UP was acquiring UP 4014 from The Southern California Chapter of The Railway and Locomotive Historical Society in Pomona, with the goal of restoring it to service. No. 4014 was moved from Pomona to the Union Pacific West Colton yard on January 26, 2014, and then to Cheyenne, Wyoming from April 28, 2014 to May 8, 2014. Restoration to full operating condition was completed in May 2019, with its first excursion called "The Great Race to Ogden" taking place during the same month.^[32]

One steam locomotive, which previously operated in excursion service, has since been retired:
UP 3985: a 4-6-6-4 Challenger class dual-service steam locomotive, operated in excursion service from 1981 to 2010 and currently retired as of January 2020. Delivered in 1943, it operated in revenue service until it was withdrawn from service in 1962. Following retirement, it was stored in the UP roundhouse until 1975, when it was moved to the employees' parking lot outside the depot in Cheyenne, Wyoming. It sat on display until 1979, when a team of employee volunteers restored it to service in 1981.^[33] Following the restoration, it was the largest operating steam locomotive in the world until it lost the title to UP 4014. In 2007, it underwent repairs for service, and was back up and running in 2008 to continue its run, but further mechanical problems caused it to be placed back into storage in October 2010. It was subsequently retired in January 2020 following 4014's restoration and is now stored at the roundhouse in Cheyenne.