Method for operating a gas turbine and gas turbine

The invention relates to a method for operating a gas turbine (10), wherein a CO2-containing gas is compressed in a compressor (13), the compressed gas is used to burn a fuel in at least one subsequent combustion chamber (14, 18), and the hot combustion gases are used to drive at least one turbine (17, 21). An improved control and performance is achieved by measuring the species concentration of the gas mixture flowing through the gas turbine (10) at several points within the gas turbine (10) by means of a plurality of species concentration sensors (22; 22a-I; 23) provided in a distributed arrangement, and utilising the measured concentration values to control the gas turbine (10) and/or optimise the combustion performance of said gas turbine (10).