Oil used for lubrication for any gear box or gear system is known as gear oil.Basically gear oil may divided into two types.
Industrial Gear Oil:
In different industrial operation there need to transmit power or any industrial parts.
For example, in steel industries mega size gears are used for rolling mill and these gear may be bevel spur & any types hypoid gear.This gear need to lubricate & these are industrial gear oil.Generally Industrial gear oils have only ISO VG grade such as ISO VG 68 or 150.
Automotive gear oil:
In automotive vehicle gear also needed,that would be differential or axle. Generally automotive gear oils are multi grade such as 80W90 or 85W140.
What is hypoid gear Oil?
In both Industrial & automotive most commonly used gear is hypoid gear.Mainly hypoid gear is transmit power in 90 degree direction.It consists of Spiral bevel & worm gear and both gear’s axis never intersect. For hypoid gear lubricants needs a special requirements,that is EP(Extreme Pressure) additives which helps lubricants to absorb extra pressure.And for this in most cases gear oil name contains EP. Hypoid gear also mandatory to automobile as need to transmit power from shaft to flywheel.