Some experts have been quick to predict apocalypse, painting grim pictures of 1,000 miles of irreplaceable wetlands and beaches at risk, fisheries damaged for seasons, fragile species wiped out and a region and an industry economically crippled for years.

President Obama has called the spill “a potentially unprecedented environmental disaster.” And some scientists have suggested that the oil might hitch a ride on the loop current in the gulf, bringing havoc to the Atlantic Coast.

Yet the Deepwater Horizon blowout is not unprecedented, nor is it yet among the worst oil accidents in history. And its ultimate impact will depend on a long list of interlinked variables, including the weather, ocean currents, the properties of the oil involved and the success or failure of the frantic efforts to stanch the flow and remediate its effects.

As one expert put it, this is the first inning of a nine-inning game. No one knows the final score.

The ruptured well, currently pouring an estimated 210,000 gallons of oil a day into the gulf, could flow for years and still not begin to approach the 36 billion gallons of oil spilled by retreating Iraqi forces when they left Kuwait in 1991. It is not yet close to the magnitude of the Ixtoc I blowout in the Bay of Campeche in Mexico in 1979, which spilled an estimated 140 million gallons of crude before the gusher could be stopped.

And it will have to get much worse before it approaches the impact of the Exxon Valdez accident of 1989, which contaminated 1,300 miles of largely untouched shoreline and killed tens of thousands of seabirds, otters and seals along with 250 eagles and 22 killer whales.

No one, not even the oil industry’s most fervent apologists, is making light of this accident. The contaminated area of the gulf continues to spread, and oil has been found in some of the fragile marshes at the tip of Louisiana. The beaches and coral reefs of the Florida Keys could be hit if the slick is captured by the gulf’s clockwise loop current.

But on Monday, the wind was pushing the slick in the opposite direction, away from the current. The worst effects of the spill have yet to be felt. And if efforts to contain the oil are even partly successful and the weather cooperates, the worst could be avoided.

“Right now what people are fearing has not materialized,” said Edward B. Overton, professor emeritus of environmental science at Louisiana State University and an expert on oil spills. “People have the idea of an Exxon Valdez, with a gunky, smelly black tide looming over the horizon waiting to wash ashore. I do not anticipate this will happen down here unless things get a lot worse.”

Dr. Overton said he was hopeful that efforts by BP to place containment structures over the leaking parts of the well will succeed, although he said it was a difficult task that could actually make things worse by damaging undersea pipes.

Other experts said that while the potential for catastrophe remained, there were reasons to remain guardedly optimistic.

“The sky is not falling,” said Quenton R. Dokken, a marine biologist and the executive director of the Gulf of Mexico Foundation, a conservation group in Corpus Christi, Tex. “We’ve certainly stepped in a hole and we’re going to have to work ourselves out of it, but it isn’t the end of the Gulf of Mexico.”

Engineers said the type of oil pouring out is lighter than the heavy crude spilled by the Exxon Valdez, evaporates more quickly and is easier to burn. It also appears to respond to the use of dispersants, which break up globs of oil and help them sink. The oil is still capable of significant damage, particularly when it is churned up with water and forms a sort of mousse that floats and can travel long distances.

Jacqueline Savitz, a senior scientist at Oceana, a nonprofit environmental group, said that much of the damage was already taking place far offshore and out of sight of surveillance aircraft and research vessels.

“Some people are saying, It hasn’t gotten to shore yet so it’s all good,” she said. “But a lot of animals live in the ocean, and a spill like this becomes bad for marine life as soon as it hits the water. You have endangered sea turtles, the larvae of bluefin tuna, shrimp and crabs and oysters, grouper. A lot of these are already being affected and have been for 10 days. We’re waiting to see how bad it is at the shore, but we may never fully understand the full impacts on ocean life.”

The economic impact is as uncertain as the environmental damage. With several million gallons of medium crude in the water already, some experts are predicting wide economic harm. Experts at the Harte Research Institute for Gulf of Mexico Studies in Corpus Christi, for example, estimated that as much as $1.6 billion of annual economic activity and services — including effects on tourism, fishing and even less tangible services like the storm protection provided by wetlands — could be at risk.

“And that’s really only the tip of the iceberg,” said David Yoskowitz, who holds the endowed chair for socioeconomics at the institute. “It’s still early in the game, and there’s a lot of potential downstream impacts, a lot of multiplier impacts.”

But much of this damage could be avoided if the various tactics employed by BP and government technicians pay off in the coming days. The winds are dying down and the seas are calming, allowing for renewed skimming operations and possible new controlled burns of oil on the surface. BP technicians are trying to inject dispersants deep below the surface, which could reduce the impact on aquatic life. Winds and currents could move the globs of emulsified oil away from coastal shellfish breeding grounds.

The gulf is not a pristine environment and has survived both chronic and acute pollution problems before. Thousands of gallons of oil flow into the gulf from natural undersea well seeps every day, engineers say, and the scores of refineries and chemical plants that line the shore from Mexico to Mississippi pour untold volumes of pollutants into the water.

After the Ixtoc spill 31 years ago, the second-largest oil release in history, the gulf rebounded. Within three years, there was little visible trace of the spill off the Mexican coast, which was compounded by a tanker accident in the gulf a few months later that released 2.6 million additional gallons, experts said.

“The gulf is tremendously resilient,” said Dr. Dokken, the marine biologist. “But we’ve always got to ask ourselves how long can we keep heaping these insults on the gulf and having it bounce back. As a scientist, I have to say I just don’t know.”

Leslie Kaufman contributed reporting from New Orleans.

(By JOHN M. BRODER and TOM ZELLER Jr., NYT, 06/05/2010)