Pseudomonas mendocina strain 0806 isolated from oil|contaminated soil was found to produce medium chain length polyhydroxyalkanoates (mcl PHAs). The mcl PHAs consist of monomers with even numbers of carbon atoms such as hydroxyhexanoate (HHx or C6), hydroxyoctanoate (HO or C8), and/or hydroxydecanoate (HD or C10) as major compositions when the strain was grown on unrelated carbon sources such as glucose, citric acid and related carbon sources such as octanoate, myristic acid or oleic acid. While even and odd number hydroxyalkanoate (HA) monomers were synthesized when tridecanoic acid was used as carbon source. The molar ratio of carbon to nitrogen ( R C/N ) had strong effects on PHA compositions: the strain produced PHAs with 97%-99% (molar ratio) HD (C10) monomer when grown in a glucose ammonium sulfate medium of R C/N <20; while 20% HO and 80% HD (molar fraction) were found as compositions in the polymers when growth was conducted in the media containing R C/N >40. It was demonstrated that the molar ratio of HO/HD remained constant in the polymers synthesized from media containing a constant R C/N , regardless of the change of glucose concentration. Up to 3 6 g/L cell dry weight containing 45% (mass fraction) PHAs was produced by the strain grown for 48?h in a medium containing 25?g/L glucose with R C/N of 40.  Pseudomonas mendocina strain 0806 isolated from oil | contaminated soil was found to produce medium chain length polyhydroxyalkanoates (mcl PHAs). The mcl PHAs consist of monomers with even numbers of carbon atoms such as hydroxyhexanoate (HHx or C6), hydroxyoctanoate (HO or C8), and / or hydroxydecanoate (HD or C10) as major compositions when the strain was grown on unrelated carbon sources such as glucose, citric acid and related carbon sources such as octanoate, myristic acid or oleic acid. While even and odd number hydroxyalkanoate (HA) monomers were synthesized when tridecanoic acid was used as carbon source. The molar ratio of carbon to nitrogen (RC / N) had strong effects on PHA compositions: the strain produced PHAs with 97% -99% molar ratio HD C10) monomer when grown in a glucose ammonium sulfate medium of RC / N <20; while 20% HO and 80% HD (molar fraction) were found as compositions in the polymers when growth was conducted in the media containing R C / N> 40. It was said that the molar ratio of HO / HD remained constant in the Synthesis of media from a constant RC / N, regardless of the change of glucose concentration. Up to 3 6 g / L cell dry weight containing 45% (mass fraction) PHAs was produced by the strain grown for 48? h in a medium containing 25? g / L glucose with RC / N of 40.