Our results demonstrate that commercially available carrageenans show significant variation with regards to the structure of the polysaccharides as well as with regards to the cations in the carrageenan samples. Furthermore, the carrageenan type specified by the manufacturers is not always in agreement with the actual molecular structure. Furthermore, our results suggested that the investigated λ-carrageenans, as well as one ι-carrageenan and two unspecified carrageenans, were actually hybrid carrageenans with κ-, ι-, and (in part) ν-units. Therefore, a detailed structural characterization is essential when carrageenans are purchased to investigate structure function relationships. Otherwise, the properties cannot be related to specific structural elements and false conclusion might be drawn about the physiological and technological effects of carrageenans. This was further supported by the rheological characterization. In absence of calcium ions, no gelation was observed. In contrast, the addition of CaCl2 at a final concentration of 0.1 M induced gel formation in all samples, except of samples LC1 and C1. The formed gels displayed considerable variations in their characteristics.