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Oil shale is a critical strategic energy with huge reserve. The research and development of an economically feasible in-situ retorting technology for oil and gas extraction from oil shale is of great significance. Thus, this paper experimentally studied the large oil-shale samples pyrolysis by in-situ superheated steam injection (MTI) implemented from 2014 to 2016. The structure of the large-scale in-situ pyrolysis test system, the experimental procedure, and the results are presented here. The steam fracturing-connection was used during the initial stage, and the pressure of the superheated steam for fracturing was ~2 times higher than the strata stress. The variation of temperature and pressure during pyrolysis was controlled by the variation in steam seepage. The operating steam pressure during pyrolysis was lower than 1/4 of the strata stress. The energy utilization of the superheated steam for the pyrolysis reaction was 42.7%. The average temperature of the fluid that was discharged from the production wells was around 170 °C, which can be recycled to achieve a heat-utilization coefficient of 13.19% in commercial operations. The oil-recovery rate in the pyrolysis area exceeded 95%, and the overall oil-recovery rate reached up to 70.7% of the tested large oil-shale samples. The gas production rate and the effective energy rate of the injected steam are correlated with an exponential function. Our pilot tests indicate that the in-situ retorting technology of oil shale by MTI shows great potential for commercial operation in oil-shale formation. • A new oil shale in-situ retorting technology, MTI technology, is proposed. • This is the first pilot test on large-scale oil-shale pyrolysis by in-situ superheated steam injection throughout the world. • The operating pressure of steam during pyrolysis is lower than 1/4 of the strata stress. • The oil-recovery rate in the pyrolysis area can exceed 95%, and the overall oil-recovery rate reaches up to 70.7%. [ABSTRACT FROM AUTHOR]