  There are proposed models of contracts, technological equipment and gas
networks and methods of their optimization. The flow in network undergoes
restrictions of contracts and equipment to be operated. The values of sources
and sinks are provided by contracts. The contract models represent (sub-)
networks. The simplest contracts represent either nodes or edges. Equipment is
modeled by edges. More sophisticated equipment is represented by sub-networks.
Examples of such equipment are multi-poles and compressor stations with many
entries and exits. The edges can be of different types corresponding to
equipment and contracts. On such edges, there are given systems of equation and
inequalities simulating the contracts and equipment. On this base, the methods
proposed that allow: calculation and control of contract values for booking on
future days and for accounting of sales and purchases; simulation and
optimization of design and of operation of gas networks. These models and
methods are implemented in software systems ACCORD and Graphicord as well as in
the distributed control system used by Wingas, Germany. As numerical example,
the industrial computations are presented.
