A tip of the hat to the Biopol blog for catching this one: The LS9 corporation has announced a biologal pathway to convert sugar into alkanes.
You can read the details at the other blog; I'm just thinking about the mass balances. Sugar is CnH2nOn. Alkanes are CnH2n+2. Assuming the sugars are glucose (the cheapest feedstock), then n = 6. That means that for every molecule of sugar, 6 oxygen atoms are removed, and 2 hydrogen atoms are added (from where?). Additionally, carbon-carbon bonds are likely being made and broken as the headline refers to alkanes and not just hexane. Regardless, that is a fairly large conversion and lots of O2 is being generated. It might well be used by the normal metabolism of the cells as well, but this byproduct is certainly harmless.