A plastic container or preform includes a multilayer wall having at least one layer of polyester resin, at least one layer of barrier resin, and an adhesion-promoting material blended with the barrier resin and/or the polyester resin to promote bonding between the barrier and polyester layers. The adhesion-promoting material includes an organometallic coupling agent based upon titanium, zirconium or aluminum. The organometallic coupling agent preferably has an amino end group with an affinity for carboxylic end groups in the polyester, and preferably is selected from the group consisting of neopentyl(diallyl)oxy, tri(N-ethylenediamino) ethyl titanate, zirconate and aluminate. Coupling agents based upon titanium and zirconium are particularly preferred for containers and preforms having a clear (non-colored) wall.