The number of North Dakota "income millionaires" is growing, likely due to wealth gained from the state's oil patch, state and industry officials say.

The state Tax Department says the number of North Dakota taxpayers reporting adjusted gross income of more than $1 million rose from 339 in 2006 to 399 last year. In 2005, there were 266 income millionaires in North Dakota.

Tax Department analyst Kathy Strombeck said the jump in the number of North Dakotans with seven-figure income probably comes largely from royalties paid to mineral owners by oil companies.

"I certainly don't think they're stock market millionaires," she said Wednesday.

More telling numbers will come in 2009, with income reported for this year, Strombeck said. Oil activity in the state likely will spike the numbers, she said.

"2008 will be big," Strombeck said.

"I think she's right," said Ron Ness, president of the North Dakota Petroleum Council.

"Most of the production has really come on this year, and the prices have come on this year," Ness said. "Oil production has gone up 88 percent in North Dakota since 2005, and a lot of it has come on within the past year."

Strombeck said the average adjusted gross income in the state increased from $43,334 on 2006 returns to $48,590 on 2007 returns. The number of returns jumped from 339,000 to 347,000 during those years, and the reported income increased $14.6 billion to $16.8 billion, she said.

Ness said the oil industry has helped bump wages throughout the state and created hundreds of high-paying jobs. It also has a domino effect on other industries, he said.

"The making of millionaires is a great story, but the story about the higher wages and more jobs is a much better one," Ness said.

Ness said the "frantic pace" of the state's oil patch will face a "calming effect" in time, but he is reluctant to talk boom-bust.

"When oil goes up, nobody knows how high oil will go up, and when oil goes down, nobody knows how far it will go down," he said.