Volume 2 of The X-Files Mythology collection is the second DVD release containing selected episodes from the third to the fifth seasons of the American science fiction television series The X-Files. The episodes collected in the release form the middle of the series' mythology, and are centered on the discovery of a mind-altering extraterrestrial "black oil".
The collection contains five episodes from the third season, eight from the fourth season, and two from the fifth. The episodes follow the investigations of paranormal-related cases, or X-Files, by FBI Special Agents Fox Mulder (David Duchovny) and Dana Scully (Gillian Anderson). Mulder is a believer in the paranormal, while the skeptical Scully has been assigned to debunk his work. Events covered in the episodes include the assassination of a secretive informant, Scully's diagnosis with cancer and Mulder's apparent suicide.
Production for many of the episode's included in the collection required extensive effects. The titular black oil's on-screen appearance was achieved through visual effects; the shimmering oil effect was digitally placed over the actors' corneas in post-production. Steven Williams, William B. Davis, Mitch Pileggi and Laurie Holden all play supporting roles in the collection. Released on August 2, 2005, the collection received mostly positive reviews from critics.