Methods and systems for operating a gas turbine engine system are provided. The system includes a fuel control system. The fuel control system includes a plurality of sensors positioned about the gas turbine engine system and configured to measure at least one parameter associated with the sensor, and a processor programmed to receive a signal from at least one of the plurality of sensors indicative of a composition of the fuel. The processor is further programmed to determine the physical properties of a fuel at an inlet to the flow control devices using a flow model and the at least one signal, determine a corresponding correction to a gas fuel flow gain using the determined physical properties, and automatically control fuel delivery as well as fuel split between the fuel injection points on the combustor using the adjusted flow gain to facilitate permitting a relatively large variation in the fuel composition for use in the gas turbine engine.