Abstract. Spontaneous formation of toroidal flow shear was identified for the first time in oblate FRCs of TS-3 and 4 experiments. Their velocities around 10 km/sec were found to peak around the magnetic axes. In high-s FRC (averaged number of ion gyro-radius ``s'' 4.5) with low velocity, its n=1 mode kept growing, causing collapse of the whole configuration. However, in low-s FRC ( s 3) with fast flow, the rotating n=2 mode became dominant after n=1 mode saturation. The spontaneous formation of flow shear possibly transformed the n=1 mode into the n=2 rotational mode, suggesting a new flow-shear stabilization of n=1 mode. The forced generation of flow shear was also demonstrated using the ``sling shot'' effect of the counterhelicity reconnection. The n=1 and 2 mode amplitudes were reduced by factor 5-10 due to the shear-flow. A new continuous generation of shear flow is being demonstrated for the stabilization and heating of FRC by use of multiple (more than two) merging of spheromaks with opposing Bt.