Cars, trucks, machinery.
Gear oil is a lubricating oil specifically for transmissions, transfer cases, and differentials in automobiles, trucks, and other machinery.
Because gear boxes don't have pumps to distribute the oil to the many moving parts, gear oil has a high viscosity to better protect the gears and usually is associated with a strong sulfur smell. This is necessary since the devices needing this heavy oil do not have pumps for transferring the oil with only a portion of the lowermost gears bathed in an oil sump.
It is important to maintain the gear oil at the upper limit on the dipstick, but never go beyond that maximum line.
This heavy oil can create viscous drag that lead to inefficiencies in vehicle operation. Some modern automatic transaxles do not use a heavy oil at all but lubricate with the lower viscosity hydraulic fluid, which you can also buy from us here.