Oily solutions are simple liquid dosage forms which allow parenteral application of active pharmaceutical ingredients (API) that are poorly soluble or unstable in aqueous systems. Additionally, release of APIs from these formulations is extended, which makes their application significantly less frequent. This property makes oily solutions especially suitable for the treatment of chronic diseases, as well as diseases characterised by variable patient adherence. Among the currently developed in vitro release methods, there are no standardised methods for the analysis of drug release in vitro from oily solutions. This paper describes the development of such method using the simple and widely available paddle apparatus (USP II) with addition of dialysis bags. The potent glucocorticoid dexamethasone was chosen as the model drug for the development of this method. Solubility of dexamethasone was examined in five vegetable oils and their mixtures with isopropanol as a cosolvent. Isopropanol has not yet been used as a cosolvent in oily solutions, but has demonstrated good solubilization properties. The highest solubility of dexamethasone was measured in the mixture of castor oil and isopropanol in a volume percentage of 20 %, with an apparent partition coefficient indicating a potential for extended release of dexamethasone from this formulation, which was consequently chosen as the model formulation for the development of this in vitro release method. Optic fiber assisted UV-Vis spectrophotometry was used to determine the amount of released dexamethasone. This setup enabled complete automatization of the in vitro release method with ensured sink conditions throughout the experiment, as there was no need to sample the release medium due to the fact that the fiber optic probe is immersed in the dissolution medium for the whole duration of the experiment. The developed in vitro release method has shown appropriate sensitivity regarding parameters that might change in vitro or during the manufacturing process (temperature and agitation rate), as well as satisfactory repeatability, simplicity and complete automatization. Therefore, the developed method can be a useful tool for the analysis of in vitro release from oily solutions during preformulation investigations as well as development of new formulations.