Brazilian natural gas industry growth has been led by electricity supply. As hydro plants generate at lower costs, thermal units only produce when hydro electricity is insufficient. This makes natural gas consumption highly volatile: Either all thermal units generate together or don’t. When all units generate together, the gas trader has to buy LNG - Liquified Natural Gas at the spot market incurring price risk. This risk can be mitigated in case the gas trader is able to sell flexible contracts to the industrial sector that can be interrupted in case of thermal generation. Thus the gas volume sold under flexible contracts is used either by thermal generation or by the industrial sector, virtually reducing total demand and avoiding emergency LNG purchases. The determination of the optimal price for these contracts is the aim of this dissertation. The determination model proposed will try to maximize a convex combination of CVaR - Conditional Value at Risk NPV - Net Present Value and trader´s profit NPV.