The delivery of gas from the national transmission system into the reg
ional supergrids, at the correct pressure, ir accomplished using a fac
ility referred to in the industry as an above-ground installation (AGI
). Early attempts to control such systems were compromised by inadequa
te models developed to explain system behaviour. This paper outlines t
he construction of a multi-input multi-output system model which has b
een used successfully to explain system operation to gas engineers as
well as providing a basis for the design and implementation of a numbe
r of advanced control systems. (C) 1996 by Elsevier Science Inc.