It is the third greatest number of outages in Entergy's 95-year history, only topped by the 1.1 million customers who lost power during Katrina and 800,000 customers who lost power a few weeks later when Hurricane Rita struck.
Nearly all of the outages were in Louisiana with smaller numbers of customers losing power in the states east of Louisiana. The storm was expected to push west toward Texas, where the wind was beginning to accelerate and the rain had just begun.
"It's not as strong as originally projected and that's good news," said Entergy spokesman Mike Burns. "But we are experiencing extremely significant damage in areas."
Power, though, was already being restored. Entergy said nearly 30,000 customers in New Orleans already have been brought back online. The company said it did not know how long it would take to restore power to the rest of the customers.
Cleco Corp., which has 273,000 customers in the state, said about 185,000 were without power and those outages were also spreading. Dixie Electric Membership Corp. reported on its Web site that 94,000 customers were without power.
Burns said 9,000 Entergy personnel, contractors and hardhats from other utilities were on standby, waiting for the worst of the storm to pass before they could begin to assess the damage.
Entergy said 134 transmission lines and 78 substations were out of service. Its nuclear plant near New Orleans was shutdown in anticipation of heavy winds.
It was not clear how or if the outages would affect the oil refineries that dot the coast.
In southeast Texas, hammered by Rita that struck right after Katrina in 2005, Entergy Texas officials were hopeful that the storm would continue to weaken.
"It's turning out to be less than what we had anticipated," said Joe Domino, Entergy Texas' president and chief executive.
Further east, Mississippi Power reported about 8,000 customers were without power and other Southern Co. utilities in Alabama and the Florida Panhandle reported outages totaling about 8,000.
"I think rebuilding and strengthening our distribution and transmission system over the past two seasons since Katrina hopefully has aided in minimizing the impact of Gustav," Mississippi Power spokeswoman Cindy Duvall said.
In April, Louisiana regulators approved a $1 billion plan from two units of Entergy to cover hurricane repair costs from Katrina and Rita in 2005 and set up a storm reserve fund. Entergy has received permission to pass along the costs to customers.
One of Entergy's utilities, Entergy New Orleans filed for reorganization under Chapter 11 of the U.S. Bankruptcy Code in October 2005. The company emerged 20 months later with a plan that paid off all creditors. The utility also received $200 million in federal funding for part of its storm recovery costs.
Meanwhile, telecommunications companies said they too were prepared for outages.
They advised customers that text messaging has a greater success rate in getting through network during high-usage periods versus voice calls. They asked that phone calls should be kept short.