A combined structural/conformational study of ethylene oxide/propylene oxide (EO/PO) copolymers has been undertaken. Electrospray ionisation (ESI) and matrix-assisted laser desorption/ionisation (MALDI) methods have been utilised and ESI-tandem mass spectrometry (MS/MS) product ion spectra, including accurate mass measurements, utilised to establish fragmentation pathways. This has enabled end group and sequence information to be obtained. Ion mobility mass spectrometry experimental, along with theoretical, approaches has been used in tandem to probe the gas-phase conformation of selected cationised species from the block and random copolymers. The cross-sections established from these measurements and calculations have been shown to be dependent on molecular weight of the oligomer and radii of the cation but largely independent of the sequence of the ion in the gas-phase. The ion mobility results have been used to aid the understanding of the fragmentation of these copolymers by means of ESI-MS/MS.