The case study is explaining the principle of long term OTC swap contracts on price or margin through examples. These swaps define a bandwidth, and sometimes a two-levels bandwidth, where volatility is exchanged against fixed price or gross margin. And swap participants are also designing « market adjusters » when markets fluctuations are extreme, but weakening the economic stabilizing effect of the OTC contract. It is recommended as a public policy to support mutual funds (or equivalent instruments) for handling extreme market events as « market adjusters »