It is now commonly accepted that the fractional valence band offset in the GaAs/ AlxGal-xAs material system lies in the region 0.3-0.4. This has important consequences for quantum well structures in which the bar Kier material is indirect (x > 0.45). If the GaAs width L is sufficiently small (Lz < 30Å) then for GaAs/AlAs quantum wells the lowest confined electron state of the system is at the X minima of the AlAs. This leads to so-called type II recombination involving electrons in the AlAs and holes in the GaAs. We have performed an extensive investigation of such phenomena on a number of GaAs/AlAs multiple quantum well structures where Lz < 30Å, using the techniques of photoluminescence (PL) and photoluminescence excitation spectroscopy (PLE). In the PL spectrum we observe both type I recombination; that is recombination of electrons and holes confined in the GaAs, and also a series of lines associated with the type II process. Using PLE we have identified the lowest confined exciton state of the type II system and combining this information with the temperature dependence of the type II PL spectra we ascribe the highest energy emission at 6K as due to the recombination of localised excitons. Further-more, absorption edges associated with higher lying (n>1) electron states confined at the X minima in the AlAs are observed in the PLE spectrum. These have relative strength and position which are in good agreement with theoretical predictions. Combining these results with a calculation of the type II exciton binding energy has led us to determine the fractional valence band offset to lie in the range 0.33-0.34.