Gas turbine with fuel composition control

The invention refers to a method for operating a gas turbine plant. According to the method a first fuel gas (5) with a first fuel reactivity and a second fuel gas (14) with a second fuel reactivity which is higher than the first fuel reactivity are injected into a combustor (4, 15) of the gas turbine, and the ratio of the mass flows of the second fuel gas (14) to the first fuel gas (5) is controlled depending on the combustion behavior of the combustor (4, 15). The disclosure further refers to a gas turbine plant configured to carry out the method.