MaldI-ToF-MS mass spectra of copolymers contain a lot of information on both chain-length distribution (CLD) and chemical composition distribution (CCD). In this paper, two random solventless liquid oligoesters were synthesized by an esterification of 1,4-butanediol with adipic acid and isoplithalic acid or glutaric acid, respectively. The thus obtained oligoesters contain two different repeat units and may therefore be regarded as a copolymer. A copolymer fingerprint analysis has been used to study the microstructure of the copolymers for which it was observed that the copolymers can be described very well using Bernoullian chain statistics.