After a careful reading of the classical concepts of market equilibrium and the process of negotiation, as well as after a of thorough study of the contemporary theories of dynamic equilibrium of markets and contracts among agents, in this work  we propose models of static and dynamic disequilibrium. The theory of disequilibrium presents the trade exchange as a balance between the sequential spot markets and the long-term contracts and is an alternative of the dominating paradigm of the market equilibrium. It provides powerful tools for implementing large and complex empirical investigations. In particular, it is useful for solving the problems, accompanying the natural gas trade, in which spot markets and long-term contracts coexist.

We describe the models and then we comment on their application to the gas sector.