Some greases are labelled "EP", which indicates "extreme pressure". Under high pressure or shock loading, normal grease can be compressed to the extent that the greased parts come into physical contact, causing friction and wear. EP grease contains solid lubricant, usually Molybdenum Disulfide, to provide protection under heavy loadings.
Molybdenum Disulfide is an inorganic compound with the formula MoS2. Its reactivity is low, rendering it resistant to dilute acids. In terms of its appearance and feel, Molybdenum Disulfide is similar to graphite and, like graphite, it is widely used as a solid lubricant. It is often incorporated as a component of blends and composites where low friction is sought.