A series of poly(ethylene ether carbonate) diol oligomers were synthesized from ethylene carbonate (EC) using various catalysts and low EC:initiator molar ratios. The structures of these oligomers have been studied by alkaline degradation to the poly(ethylene glycol)s, which make up their backbone, followed by capillary gas chromatographic (CGC) analysis. Comparisons of CGC traces before and after hydrolysis indicate which volatile components contain carbonate moieties. Some poly(ethylene glycol)s were not chemically bound into the polymer backbone and were analyzed directly by CGC. Based on the combination of analytical techniques developed in this study, it is possible for the first time to establish the approximate composition of a given poly(ethylene ether carbonate) diol. A typical composition made using a sodium stannate trihydrate catalyst consists of (1) an oligomeric portion which is a copolymer of carbon dioxide and poly(ethylene glycol)s and (2) a monomeric portion which consists mostly of diethylene glycol with lesser quantities of monoethylene glycol, triethylene glycol, 1,4-dioxane and unreacted ethylene carbonate.