In this paper, we discuss stationary time- and frequency-selective channels. No channel 
knowledge is assumed, neither at the transmitter nor at the receiver. We investigate the 
capacity behavior of these doubly selective channels and in particular the role of the key 
channel parameters delay spread, Doppler bandwidth and channel spread factor (the product 
of delay spread and Doppler bandwidth) which govern the capacity behavior at high values 
of signal to noise ratio (SNR). Different capacity regimes of capacity where the dominant 
term of capacity is log(SNR) or log[log(SNR)] and channel conditions (delay spread, Doppler 
Bandwidth and channel spread factor) are specified which govern in which regime the capacity 
will be operating. For critically spread channels (channel spread factor of 1), it is widely 
believed that the dominant term of the high-SNR expansion of the capacity is log[log(SNR)] 
or in other words, the pre-log (the coefficient of log(SNR)) is zero. We give a very simple 
scheme which shows that even for critically spread channels a non-zero pre-log exists under 
certain conditions on Doppler bandwidth and delay spread. Furthermore, we also show that a 
pre-log may exist even for over-spread channels (channel spread factor greater than 1). For 
a specific larger channel spread the log[log(SNR)] regime takes over for which we provide 
bounds on the pre-loglog.