JACKSONVILLE, Fla. -- Sales of Bibles and books on prophecy are on an upswing that began soon after the terrorist attacks last month and is expected to continue through Christmas, industry leaders say.

"Any time you have a tragedy like this one, there's something of a vacuum that develops in people's hearts," said Cris Doornbos, an executive of Michigan-based Zondervan, one of the world's largest publishers of Bibles and Christian books. "They certainly turn to religion because they believe it is something of a bedrock."

Worried parents are among those coming in to buy Bibles, said Sherrie Austin, who works as a sales clerk at Berean Christian Store in Jacksonville.

"They are trying to get their children something to stand on," she said.

Berean Christian Stores have sold 30 percent more Bibles this year than at this time last year, said Gene Ross, district manager for stores in Florida and Georgia.

"I guess this makes you stop and think," said Diana Triplett, buying a Bible for her college-aged son at a Berean Christian Store.

Bible sales were up 27 percent for Family Christian Stores, company president Les Dietzman said. Books on prophesy were hardly selling before Sept. 15, he said. Now, sales are up 80 percent.

"Customers are asking for anything to do with end times," said Angel Stapler, general manager of a Jacksonville Books-A-Million store. "We are replenishing our supplies constantly."

Books from an already popular "Left Behind" series by Jerry Jenkins and Tim LaHaye are in high demand, she said.

"People are unsettled and unsure and they want to know how events like this play in the bigger picture," said Rolf Zettersten, vice president of Warner Books, an AOL Time Warner company. "They turn to authors who can interpret scripture and prophesy to find some kind of comfort and explanation."

Sales of religious books also spiked during the 1991 Gulf War, according to Doornbos.