The Deepwater Horizon rig stands about 80 kilometres off the Louisiana coast. ((Gerald Herbert/Associated Press))

Cleanup crews are tipping dispersant into the Gulf of Mexico in a bid to sink oil spilled from a drilling rig that sank Thursday off the Louisiana coast.

"The oil slick is made of two components," explains CBC science commentator Bob McDonald.

"There's diesel, which is from the rig itself. They're not too worried about that, because diesel is very, very light. It floats on the surface and it will just evaporate into the air. The crude oil is coming from the well itself."

A search of the sunken rig using underwater robots has revealed the rig is not currently leaking, according to the U.S. coast guard.

The dispersant, like a detergent, will make the oil slick sink. McDonald notes, however, that this solution will affect underwater life in the Gulf. 

"Now it's going to be on the bottom of the Gulf," he said. "There are critters that live down there, too. There's crabs and mussels and worms and all kinds of things in the mud. They'll have to deal with these bowling ball-shaped globules that will be rolling around on the sea floor."

Meanwhile, workers are moving quickly, as the threat of changing winds and currents could push oil toward the vulnerable coastal wetlands that house fish, shrimp and birds.

Here is a by-the-numbers look at the sunken oil rig and the cleanup effort:

  • The Deepwater Horizon oil rig was situated about 80 kilometres off the Louisiana coast.
  • The rig, owned by Transocean Ltd. and under contract to the oil giant BP, burned for 36 hours before sinking.
  • Deepwater Horizon measured 122 metres by 76 metres, about twice the size of a football field.
  • More than 100 workers were rescued from the rig. Four people were injured and 11 are missing.
  • About 100,000 gallons of dispersant will be poured into the Gulf of Mexico.
  • On Friday, the slick measured 16 km by 16 km on the ocean surface.
  • BP PLC, the oil company that leased the rig, said they are sending out 32 vessels — capable of sucking up 171,000 barrels of oil daily — to mop up the messy slick.
  • About 1.8 million migratory waterfowl use the Louisiana's coastal wetlands as a habitat.