BP Cleaning Up the Oil Spill Better than thought

* 26 pct remains as sheen or tarballs, buried or onshore

* One-fourth of oil naturally evaporated or dissolved

* Burning, skimming and collection garnered another fourth (Adds Senate hearing on dispersants, paragraphs 10-12, edits)

By Deborah Zabarenko, Environment Correspondent

WASHINGTON, Aug 4 (Reuters) - Nearly three-fourths of oil from the BP (BP.L)(BP.N) spill is gone from the Gulf of Mexico, with 26 percent remaining as a sheen or tarballs, buried in sediment or washed ashore, U.S. scientists said on Wednesday.

"It is estimated that burning, skimming and direct recovery from the wellhead removed one quarter (25 percent) of the oil released from the wellhead," the scientists said in the report "BP Deepwater Horizon Oil Budget: What Happened to the Oil?"

Another 25 percent naturally evaporated or dissolved and 24 percent was dispersed, either naturally or "as the result of operations," into small droplets, the report said.

The rest of the estimated 4.9 million barrels of crude spilled into the Gulf after the April 20 rig explosion that triggered the leak is either on or just beneath the water's surface as "light sheen or weathered tarballs," has washed ashore where it may have been collected, or is buried in sand and sediments at the sea bottom.

The report found 33 percent of the oil has been dealt with by the Unified Command, which includes government and private efforts.

"This includes oil that was captured directly from the wellhead by the riser pipe insertion tube and top hat systems (17 percent), burning (5 percent), skimming (3 percent) and chemical dispersion (8 percent)," the report found.

Natural processes broke down the rest of the 74 percent that has been removed from the Gulf.

"The good news is that the vast majority of the oil appears to be gone," Carol Browner, energy and climate change adviser to President Barack Obama, said on ABC's "Good Morning America." "That's what the initial assessment of our scientists is telling us."

"We do feel like this is an important turning point," she said.

The report was released just before officials from the National Oceanic and Atmospheric Administration and the Environmental Protection Agency testified at a U.S. Senate hearing about the use of dispersant chemicals to combat the BP spill.

Paul Anastas, of EPA's office of research and development, acknowledged there are "environmental tradeoffs" to consider when using dispersants.

Anastas told the Senate Environment and Public Works Committee that dispersants are generally less toxic than oil, cut the risk to shorelines and degrade quickly, in days or weeks.