What does the acronym EP stand for in oil additive terminology?

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EP stands for Extreme Pressure. This term refers to oil additives that protect metal surfaces when load is very high and the lubricating film is thin, by forming a protective film at the contact interfaces. The chemistry often involves sulfur- or phosphorus-containing compounds that react under high pressure to create a wear-resistant layer, reducing metal-to-metal contact and scoring in boundary lubrication conditions. You’ll see EP additives used in gear oils, heavy-duty applications, and some engine oils for severe service. The other phrases don’t fit because they describe electrical pressure or performance outcomes rather than the chemical class of additives providing high-load protection.