Abstract-This correspondence studies linear receivers for MIMO channels under frequency-nonselective (flat) quasi-static Rayleigh fading. The outage probability and diversity gain of MMSE and Zero Forcing (ZF) receivers are investigated. It is found that contrary to intuition, MMSE and zero-forcing receivers may not perform similarly at high SNR. Assuming M transmit and N receive antennas, the zero-forcing receiver always has diversity N −M +1, unlike the MMSE receiver, whose behavior can vary. Under separate spatial encoding, where data from each transmit antenna is separately encoded, MMSE is no better than ZF in terms of diversity. But for joint spatial encoding systems, where an encoded stream is sent from all the antennas, the MMSE receiver achieves diversity M N at low spectral efficiencies but has diversity only M − N + 1 at high spectral efficiencies.