Although the government has been slow to say what's happened to it, a picture can be drawn from a publicly available model called the Automated Data Inquiry for Oil Spills.
The model shows that about 35 percent of a hypothetical 4.8 million gallon spill of light Louisiana crude oil released in conditions similar to those found in the Gulf now would evaporate.
It also shows that between 50 percent and 60 percent of the oil would remain in or on the water and the rest would be dispersed in the ocean.
Ed Overton, a Louisiana State University chemist analyzing the spill, says he thinks most of the oil is floating within 1 foot of the surface.
Authorities are testing suspected "tar balls" found on Mississippi shores to see if they came from the oil spill in the Gulf of Mexico. Dan Turner, a spokesman for Gov. Haley Barbour, said "very sparsely scattered, small tar balls" were found in recent days on the beaches of West Ship Island, Horn Island, Pass Christian and Long Beach.
Turner said the substance may have came from controlled burns on the oil gushing from the site of an April 20 rig explosion.
A small piece of boom with an "oily substance" also was found on the Mississippi coast. Turner said authorities are trying determine where it came from and if it had oil on it from the spill. Tar balls also have turned up in Alabama and Louisiana.