Rising maritime traffic and activities have caused oil pollution of the marine environment to increase considerably in recent decades, with illegal dumping of bilge water from ships being one of the main sources of this type of pollution. Numerous studies have established that the main hydrocarbons found in seawater are n-alkanes from diesel and polycyclic aromatic hydrocarbons (PAHs). This source of pollution could be reduced through the installation, on the vessels themselves, of systems that allow the degradation of hydrocarbons. Advanced oxidation processes are of great importance as techniques for the degradation of organic pollutants, among which ozonation stands out. In this context, the aim of this work was to establish the effectiveness of ozonation to oxidise n-alkanes contained in diesel and PAHs declared by the EPA as priority pollutants in seawater. For this purpose, artificial seawater was prepared and contaminated with one of the two types of hydrocarbons of interest and the samples were then subjected to an ozonation process. After ozonation, the samples were extracted by SPME and then analysed by GC-MS. The results show that, under the conditions of this study, ozone was able to degrade 94.6% of the total PAHs in only 60 minutes, however, longer ozone exposure times (720 minutes) were needed to degrade 87.3% of the total n-alkanes present in the medium. It is noteworthy that, for both, PAHs and diesel, only 100% oxidation of the lower molecular weight compounds was achieved, therefore for the heavier compounds more aggressive oxidation conditions should be applied.