Measurement of lubricity
The lubricity of a substance is not a material property, and cannot be measured directly. Tests are performed to quantify a lubricant's performance for a specific system. This is often done by determining how much wear is caused to a surface by a given wear-inducing object in a given amount of time. Other factors such as surface size, temperature, and pressure are also specified. For two fluids with the same viscosity, the one that results in a smaller wear scar is considered to have higher lubricity. For this reason lubricity is also termed a substance's anti-wear property.
Examples of test setups include "Ball-on-cylinder" and "Ball-on-three-discs" tests.
Lubricity in diesel engines
In a modern diesel engine, the fuel is part of the engine lubrication process. Diesel fuel naturally contains compounds that provide lubricity, but because of regulations in many countries (such as the US and the EU), sulphur must be removed from the fuel before it can be sold. The hydrotreatment of diesel fuel to remove sulphur also removes the compounds that provide lubricity. Reformulated diesel fuel that does not have biodiesel added has a lower lubricity and requires lubricity improving additives to prevent excessive engine wear.  
- Reformulated Diesel Fuels and Fuel Injection Equipment; Author: Hugh C. Grigg (Lucas Powertrain Systems) Presented at the New Fuels and Vehicles for Cleaner Air Conference, January 11-12, 1994, Phoenix, Arizona. (Retrieved via Google from a publication of the National Biodiesel Board, entitled Lubrication)
- Fuels for Diesel Engines — Diesel Fuel Injection Equipment Manufacturers Common Position Statement, Signed by: Delphi Diesel Systems, Stanadyne Automotive Corp., Denso Corporation, and Robert Bosch GmbH, issued June, 2000 (Retrieved via Google from a publication of the National Biodiesel Board, entitled Lubrication)
- Diesel Fuel Lubricity Authors: Paul Lacey and Steve Westbrook (Southwest Research Institute) SAE paper 950248, International Congress and Exposition, Detroit, Michigan, February 27-March 2, 1995 (Retrieved via Google from a publication of the National Biodiesel Board, entitled Lubrication)