Really, now... the white stuff is gas, which bubbles up with the oil. Black = oil, white = gas, brown = mud. Not so hard...
The VENTS Geology Program aims to understand how submarine volcanic activity affects hydrothermal venting and life in the oceans. The ultimate heat source for all hydrothermal venting is molten rock within the Earth. Individual volcanic events bring this heat close to the surface where it can be released into the ocean, along with chemicals that sustain unique biological environments, both on and below the seafloor. Therefore, we are especially interested in studying the sites of recent submarine eruptions.
NOAA - Submarine VolcanismIn more and more places, scientists are finding large amounts of natural gas on the ocean bottom: When Seafloor Meets Ocean, the Chemistry Is Amazing
National Geographic News - Deep-Sea Volcano Erupts on Film -- A First