The surface area of a catastrophic Gulf of Mexico oil spill quickly tripled in size amid growing fears among experts that the slick could become vastly more devastating than it seemed just two days ago.

Frustrated fishermen eager to help contain the spill from a ruptured underwater well had to keep their boats idle Saturday as another day of rough seas kept crews away from the slick.

President Barack Obama planned a Sunday trip to the Gulf Coast to see the damage himself.

Documents also emerged showing BP downplayed the possibility of a catastrophic accident at the offshore rig that exploded.

How far the spill will reach is unknown, but the sheen already has reached into precious shoreline habitat and remains unstopped, raising fears that the ruptured well could be pouring more oil into the gulf than estimated.

The Coast Guard has estimated that about 200,000 gallons (757,060 liters) of oil are spewing out each day _ which would mean 1.6 million gallons (6.06 million liters) of oil have spilled since the April 20 explosion that killed 11 workers. The environmental mess could eclipse the Exxon Valdez disaster, when an oil tanker spilled 11 million gallons (42 million liters) off Alaska's shores in 1989.

The slick nearly tripled in just a day or so, growing from a spill the size of Rhode Island to something closer to the size of Puerto Rico, according to images collected from mostly European satellites and analyzed by the University of Miami.

On Thursday, the size of the slick was about 1,150 square miles (nearly 3,000 square kilometers), but by Friday's end it was in the range of 3,850 square miles (9,900 square kilometers), said Hans Graber, executive director of the university's Center for Southeastern Tropical Advanced Remote Sensing. That suggests the oil has started spilling from the well more quickly, Graber said.

"The spill and the spreading is getting so much faster and expanding much quicker than they estimated," Graber told The Associated Press on Saturday.

Louisiana State University professor Ed Overton, who heads a federal chemical hazard assessment team for oil spills, cautioned that the satellite imagery could be deceiving.

He said satellites can't measure the thickness of the sheen and makes it difficult to judge how much oil is on the water.

Another issue is that the oil slicks are not one giant uniform spill the size of an island. Instead, they are "little globs of oil in an area of big water," Overton said.

One expert also cautioned that if the spill continues growing unchecked, sea currents could suck the sheen down past the Florida Keys and then up the Eastern Seaboard.

The Florida Keys are home to the only living coral barrier reef in North America, and the third largest coral barrier reef in the world. About 84 percent of the nation's coral reefs are located in Florida, where hundreds of marine species live, breed and spawn.

"If it gets into the Keys, that would be devastating," said Duke University biologist Larry Crowder.

Ian R. MacDonald, an oceanography professor at Florida State University, said his examination of Coast Guard charts and satellite images indicated that up to 9 million gallons (34 million liters) had already spilled by April 28.

However, officials with the Coast Guard brushed off such fears and said the estimates were imprecise.

BP suggested in a 2009 exploration plan and environmental impact analysis for the well that an accident leading to a giant crude oil spill _ and serious damage to beaches, fish and mammals _ was unlikely, or virtually impossible.

The plan for the Deepwater Horizon well, filed with the federal Minerals Management Service, said repeatedly that it was "unlikely that an accidental surface or subsurface oil spill would occur from the proposed activities."

The company conceded a spill would impact beaches, wildlife refuges and wilderness areas, but argued that "due to the distance to shore (48 miles, or 77 kilometers) and the response capabilities that would be implemented, no significant adverse impacts are expected."

The spill threatens hundreds of species of wildlife, including birds, dolphins, and the fish, shrimp, oysters and crabs that make the Gulf Coast one of the nation's most abundant sources of seafood.

Although the cause of the explosion was under investigation, many of the more than two dozen lawsuits filed in the wake of the explosion claim it was caused when workers for oil services contractor Halliburton Inc. improperly capped the well _ a process known as cementing. Halliburton denied it.

The Coast Guard said Saturday it had shut down two offshore platforms and evacuated one of them near the spill as a safety precaution.

BP has tried applying chemicals underwater to break up the oil before it reaches the surface. That has never before been attempted at such depths.

BP and federal authorities said the dispersant was released overnight at the site of the leak, nearly 5,000 feet (1,524 meters) underwater, and they were evaluating the effort Saturday.

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Associated Press writers Seth Borenstein, Melissa Nelson, Michael Kunzelman, Chris Kahn, Allen G. Breed, Vicki Smith, Janet McConnaughey, Alan Sayre, Tamara Lush and Brian Skoloff contributed to this report.