Refineries are made up of a number of different process units. The combination of process units that the refinery has is its configuration.

The more units a refinery has the better its ability to run lower-quality (cheaper) crudes, and to make a high proportion of light (higher-value) products such as diesel and gasoline.

Typically the configuration is described in terms of the most value-creating process unit at the refinery. For example, a refinery with a coker and a hydrocracker would likely be described as having a coking/hydrocracking configuration.

Some examples of common configuration definitions:

Topping configuration - Atmospheric distillation and hydrotreating

Hydroskimming configuration - Atmospheric distillation, with reforming and hydrotreating

Cracking configuration - Atmospheric distillation with FCC, reforming and hydrotreating

A quantitative measure of a refinery’s configuration is its complexity number. A complex refinery has a complexity number of 12-15. A simple refinery has a complexity number below 8.