Two strains of a novel bacterium were isolated independently of each other, from different depths in the Mediterranean Sea, within a time period of 7 months, using two different isolation approaches that were focused on different objectives. Both strains, designated ISO1 and ISO4T, were halophilic, Gram-negative, strictly aerobic, straight rods that were oxidase- and catalase-positive. Both strains produced mucoid colonies in some defined minimal media and were able to grow with organic acids and some alkanes; they were also able to accumulate intracellular poly-beta-hydroxybutyrate granules. The G + C content of the DNA of strain ISO4T was 66 mol%. Comparative analysis of 16S rRNA gene sequences showed that the closest described species to the novel strains were Alcanivorax borkumensis and Fundibacter jadensis, both of the gamma-Proteobacteria. Both of these recognized species were originally isolated from North Sea waters and are able to degrade aliphatic compounds, a property shared with strains ISO1 and ISO4T. However, strains ISO1 and ISO4T were different from A. borkumensis and F. jadensis, not only in their 16S rDNA sequences but also in the motility of their cells (by polar flagella) and by the presence of C19:Ocyclo in their cellular fatty acids, among other differential features. On the basis of biochemical and molecular data, it is suggested that strains ISO1 and ISO4T be recognized as a novel species of the genus Alcanivorax, for which the name Alcanivorax venustensis (ISO4T =DSM 13974T =CECT 5388T) is proposed. On the basis of its high phenotypic similarity and close phylogenetic relatedness to A. borkumensis, it is also proposed that F. jadensis (DSM 12178T) be reclassified as Alcanivorax jadensis in the genus Alcanivorax, and that the description of the genus Alcanivorax be emended.