Cyclic oligomers of poly(decamethylene terephthalate) (PDT) were prepared successfully and cleanly from a ring-chain equilibrium reaction in dilute solution of chlorobenzene. A variety of catalysts were investigated for this purpose. The reactions were monitored up to equilibrium and the molar cyclization equilibrium constants K-x deduced. Satisfactory yields of cyclics [O(CH2)(10)OCOC6H4CO](x) were obtained, together with a higher molar mass linear polymer. Mass spectroscopic investigation showed that no monomeric ring was formed in the PDT reaction. The individual cyclics with x = 2-14 corresponding to 36-252 skeletal bonds were completely resolved using PL-gel mixed-E gel permeation chromatographic columns. The lower mass cyclics (x = 2-5) were cleanly extracted and then characterized. The yield of cyclics in ring-chain equilibrates corresponding to a solvent/polymer dilution ratio of 30/1, 60/1 and 100/1 were ca 11%, ca 30% and ca 50%, respectively. The K-x values for PDT cyclics were used to compare the statistical conformations of the corresponding PDT chains in chlorobenzene with an aliphatic polyester, poly(decamethylene adipate), which was studied previously.