We present a novel adaptive transmission technique for MIMO systems with the aim to enhancing the spectral efficiency for a target error rate performance and transmit power. This adaptive method employs the condition number of the spatial correlation matrix as an indicator of the spatial selectivity of the MIMO channel. The distribution of the condition number is then used to identify the prevailing channel environment. Depending on the identified channel state, our adaptive algorithm chooses the MIMO transmission method, among spatial multiplexing, D-STTD, and beamforming, that maximizes the spectral efficiency. Performance results show significant gains in throughput and reduced error rate compared to conventional fixed transmission schemes.