A typical gas sales agreement (GSA) also called a gas swing contract, is an agreement between a supplier and a purchaser for the delivery of variable daily quantities of gas, between specified minimum and maximum daily limits, over a certain number of years at a specified set of contract prices....

This paper uses the logistic smooth transition GARCH model to study the time-varying volatility of the USS?P 500 index. In the LSTGARCH specification, the parameters are function of some information variables that help capturing the conditional return volatility. Tests of standard GARCH models...