Power allocation is an important issue for spectrum sharing of unlicensed bands, in which multiple unlicensed systems may coexist and operate. Recently some works have been reported on game theoretical analysis for multiple systems cooperating in frequency-flat unlicensed bands. However, there has not been much work on the cooperative and competitive strategic behavior of multiple mutually interfering systems in frequency- selective unlicensed bands. In this paper, we construct a game theoretical framework for multiple selfish systems on frequency- selective Interference Channels (IC). This framework enables us to utilize existing protocols designed for frequency-flat ICs in frequency-selective scenarios and can be regarded as an extension of previous results for frequency-flat scenarios.