gear oil (automotive) - long-life oil of relatively high viscosity for the lubrication of rear axles and some manual transmissions. Most final drives and many accessories in agricultural and construction equipment also require gear oils. Straight (non-additive) mineral gear oils are suitable for most hypoid rear axles (see gear) and for some manual transmissions. Use of such oils is declining, however, in favor of EP (extreme-pressure) gear oils (see EP oil) suitable both for hypoid gears (see gear) and for all straight mineral oil applications. An EP gear oil is also appropriate for off highway and other automotive applications for which the lubricant must meet the requirements of Military Specification MIL-L-2105D.