The Kra Basin is known to have over 1200 meters of excellent source rock, but it has yet to yield a commercial oil discovery. One well, the B5/27-2, has tested oil. The oil tested in that well may have come from lacustrine carbonates of Tertiary age, rather than karstified Paleozoic limestones. The reservoir interval in that well displays good sonic log porosity, which should not be the case for the Paleozoic. Lacustrine carbonates associated with the initial opening of the South Atlantic Ocean during the Cretaceous have produced hundreds of millions of barrels of oil in Angola (Malongo West and Limba Fields) and Brazil's Campos Basin (Badejo, Linguado and Pampo Fields). These carbonates are skeletal grainstones commonly described as coquina.