OTR files are used to store compiled data for UNIX-like operating system IRIX, developed by Silicon Graphics until 2006 when the project was dropped and is now considered obsolete.

OTR files store compiled and optimized data file, similar to Linux’s FTR files. CTR is the older version or OTR format no longer used since versions 6.3 of IRIX. OTR files are saved as ASCII text and start with "TYPE" entry which determines the type of given file data.