2 the interactions between the excitons are entirely dipole-dipole repulsive. In this paper, we consider the collective properties of (a) excitons within one QW in the presence of a 2D electron gas (2DEG) and (b) dipole excitons with spatially separated electrons and holes in CQWs when the number of electrons in the electron well is much larger than the number of holes in the hole well. In case (b), the system can be treated as a system of dipole excitons in the presence of a 2DEG in one well. The photoluminescence (PL) spectra caused by the recombination of 2D electrons in a single heterojunction quantum well (SHQW) result in the experimental observation of the excitons coexisting with a degenerate 2DEG in the same subband [12]. As shown by time-resolved PL measurements, an increase in the integrated PL intensity and the anomalously fast occurrence of PL from the region around the filament is induced by the screening response of the 2DEG-exciton system to the abrupt appearance of a remote photocurrent filament in the 2DEG [13]. These observations in conjunction with theory reported in this paper suggest the occurrence of fast long-range transport of excitons. We emphasize, that although the K-T transition has been investigated for 2D excitons [7, 8], the key result of our Paper is that we include the 2DEG in our considerations. Consequently, the resulting formulas for the superfluid density K-T transition temperature are a novel result which we present below. We then try to connect our theory with recent experimental results as an alternative explanation of the data. We now describe the theoretical calculations for determining the superfluid density and K-T transition temperature in a QW containing 2D excitons along with the 2DEG. There are two types of interaction in this system: exciton- exciton ( X − X ) and exciton-electron ( X − e ) interaction, while in the absence of 2DEG there is only X − X interaction. In a QW in the presence of 2DEG the X − e interaction plays an important role, since X − e scattering is twice as efficient as X − X scattering [14]. The spectrum of collective excitations (quasiparticles) in a QW containing the 2D excitons has the sound branch. This sound branch on the spectrum of collective excitations is indicative of the interaction strength of exciton-exciton ( X − X ) scattering and the energy spectrum ε$_{X}$$_{−}$$_{X}$ ( p ) in the framework of weakly non-ideal dilute Bose gas provided by Bogoliubov approximation [15, 16] is given by ε$_{X}$$_{−}$$_{X}$ ( p ) = c$_{s}$p , where c$_{s}$ = U$_{0}$n/M , p is momentum, c$_{s}$ is the sound velocity of collective branch due to X − X scattering, n is the exciton density, M = m$_{e}$ + m$_{h}$ is the exciton mass ( m$_{e}$ and m$_{h}$ are the effective masses of electron and hole, respectively), U$_{0}$ is the zero-order Fourier-component (at p = 0) of the exciton-exciton repulsion potential assuming a hard sphere approximation, given by [17] U$_{0}$ = 6 e $^{2}$a$_{2}$$_{D}$ /ϵ , where e is the electron charge, a$_{2}$$_{D}$ = ℏ $^{2}$ϵ/ (2 µ$_{e}$$_{−}$$_{h}$e $^{2}$), µ$_{e}$$_{−}$$_{h}$ = m$_{e}$m$_{h}$/ ( m$_{e}$ + m$_{h}$ ), ϵ is the dielectric constant. For the system of the spatially separated excitons and electrons in coupled quantum wells (CQWs) it was shown