Beautiful UP X-18 in all her Glory

Union Pacific operated the largest fleet of gas turbine-electric locomotives (GTELs) of any railroad in the world. The prototype, UP 50 was the first in a series built by General Electric (marketed by the Alco-GE partnership, until 1953) for Union Pacific's long-haul cargo services. The prototype was introduced in 1948 and was followed by three series of production locomotives. The turbines were used extensively; at one point Union Pacific claimed that the turbines hauled more than 10% of the railroad's freight.

Their fuel economy was rather poor, as the turbine consumed roughly twice as much fuel as an equally powerful diesel engine. This was initially not a problem, since Union Pacific's turbines were fueled by Bunker C heavy fuel oil. This highly viscous fuel was less expensive than diesel, but difficult to handle. When cold, its consistency was likened to tar or molasses. To solve this problem, a heating apparatus was built into the fuel tanks (and later into fuel tenders) to heat the fuel to 200 °F (93 °C) before being fed into the turbine. Soot buildup and blade erosion caused by corrosive ashes plagued all of the turbines. They were operated into the 1970s, when rising fuel costs made them uneconomical.

From Wikipedia 2009