For the fiscal year ended Sept. 30, 2010, the IRS examined about 18.4 percent of returns filed by the highest income demographic – people with income in excess of $10 million. That represents a significant increase from the prior year, when the same audit rate was 10.6 percent.

Overall, the IRS audits about 1,160 out of every 10,000 returns filed, according to the IRS Data Book. While examination rates for all income groups went up, with the exception of the group with no income, individuals with incomes between $75,000 and $100,000 had only a 0.64 percent chance of being audited – less than 13 returns out of every 10,000 returns filed.

The overall audit rate for corporations was 1.3 percent, rising with the size of the corporation. The IRS examined 98 percent of the tax returns filed by the largest corporations, those with assets of $20 billion or more.