Olive fruits of the Gemlik variety harvested from different regions of Turkey were placed in aseptic or non-aseptic brines containing 6 % NaCl. Olives of non-aseptic treatment were left to spontaneously ferment under anaerobic conditions. Samples for microbiological and chemical analysis were taken periodically during the course of the fermentation. No lactic acid bacteria growth was observed in three of the six samples, and yeasts were the prevailing microbial group in the other samples. Brines were analyzed for fermentable substrates (glucose, fructose, sucrose and mannitol), fermentation products (organic acids and ethanol) and phenolic-oleosidic compounds. Most of the unprocessed fruits had a low concentration of oleuropein. Hydroxytyrosol and oleoside 11-methyl ester were the main phenolic and oleosidic compounds in all brines. Likewise, the content of antimicrobials such as the dialdehyde form of decarboxymethyl elenolic acid, either free or linked to hydroxytyrosol, in brines was very low, which may permit the growth of lactic acid bacteria in these media. A growth test with two strains of Lactobacillus plantarum was applied to aseptic brines of all samples to determine whether these compounds inhibited lactic acid bacteria growth. The results of this study indicated that Gemlik olive is a "sweet" variety with a low antimicrobial compound content that can be fermented by lactic acid bacteria under favorable conditions.