Technologies used include:

Mechanical Filtration: Using filters of varying micron ratings to remove particles.
Centrifugation: Spinning oil to separate contaminants based on density.
Vacuum Dehydration: Removing water and gases under reduced pressure.
Coalescence: Aggregating small water droplets into larger ones for easier separation.
Adsorption: Using materials like activated clay to remove dissolved contaminants and oxidation products.
These technologies can be combined for comprehensive purification.