Figure 2. Probably 90% of oil formed in the sedimentary deposits of the world has migrated to the earth’s surface where it formed oil seeps and pools, and eventually disappeared altogether. Here, at the famous La Brea deposits on Wilshire Boulevard (A) in Los Angeles, California, active oil seeps from underlying Tertiary rocks form pools in Pleistocene and Recent alluvium (B). These pools, like so many others in the world, have trapped animals, plants and protists in the gooey mess. J.H. Lipps image, 2008.