The ALCO Century 636 was the most powerful single-engine diesel locomotive constructed by ALCO. The locomotive had a C-C wheel arrangement and 3600 horsepower (2.7 MW). Visually, it is almost identical to the Century 630.

34 C636s were built in 1967 and 1968. 6 went to Illinois Central, 15 to Penn Central, and 10 to Spokane, Portland & Seattle . The remaining three were used as demonstrators.

The Delaware-Lackawanna Railroad and Cartier Mining in Quebec are still operating C636s as of 2004.

(need confirmation of Cartier Mining engines)