.oil is a raster image and animation file format associated with certain old versions of the open source image processing library first named OpenIL, then DevIL (Developer's Image Library).
The OIL format was new in OpenIL 2.1.0b (2000-12-29). The last version of the software to be named OpenIL was 2.1.4b. Around 2001-06 it was renamed DevIL, and the version number was reset to 1.1.1. The last version of DevIL to support the format was 1.1.8; support for it was removed in v1.1.9 (2001-11-02).
OIL files begin with bytes
4f 49 4c 00 71 3d 69 00.
- DevIL Docs 1.1.8 → ImageLib/docs/oil_spec/index.htm
- There are a few test files in the source distribution (ImageLib/testil/windowstest/resources/*.oil).