Quenching of reactions in probes is the prerequirement in measurements of combustion performance of engines by the gas sampling. In order to quantify degrees of the quenching in the probes used for scramjet testing, we tested four kinds of gas-sampling probes, three freezing-oriented and a reaction-oriented probes using a supersonic combustor operating with an M 2.5 air flow of the temperature up to 2250K and compared the combustion efficiency (ηc) measured. The freezingoriented probes yielded gas compositions consisting of partially burned H2 and O2 even at an air temperature of 2200K. The pitot pressure indicated that the combustion took place in the supersonic combustor not in the probes. The freezing-oriented probes with the tip diameter of 0.3mm indicated the correct ηc in the scramjet combustor.