The X-Files Season 3 Episode 15

A French salvage ship searching for a lost WWII fighter plane unknowingly surfaces an alien which appears in the form of black oil and has the ability to jump hosts. Mulder heads to Hong Kong to investigate the salvage broker who sold the information to the French and he encounters Krycek, who has been selling information from the MJ documents. As Mulder prepares to take Krycek back to the US, the alien makes its way to Hong Kong and takes control of Krycek.