Measurement of lubricity
Lubricity of a material cannot be directly measured, so tests are performed to quantify a lubricant's performance. This is done by determining how much wear is caused to a surface by a given friction-inducing object in a given amount of time. Other factors such as surface size, temperature, and pressure are also specified. The greater the wear scar the worse the 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 sulfur compounds that provide good lubricity, but because of regulations in many countries (such as the US and the EU) sulphur must be removed. 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)