The Howe Group have estimated the amount of hydrocarbons produced by marine microbes.
Chris Howe's group, with an international team of researchers, have estimated the amount of hydrocarbons (the primary ingredient in crude oil) that are produced by a massive population of photosynthetic marine microbes, called cyanobacteria. These organisms in turn support another population of bacteria that 'feed' on these compounds.
In the study published in Proceedings of the National Academy of Sciences of the USA, the scientists measured the amount of hydrocarbons in a range of laboratory-grown cyanobacteria and used the data to estimate the amount produced in the oceans. You can read the full story on the University news website.