B visa is a non-immigrant visa for international visitors who wish to enter the United States temporarily for business (B-1) or for pleasure, tourism or medical treatment (B-2). Each year millions of people visit the U.S. on B visas. Unfortunately, many others saw their applications denied. The Department of State, which is responsible for issuing visas at U.S. embassies and consulates abroad, publishes an annual report on B visa refusal rate based on nationality. The table below contains the complete data (as of 9/30/10) for fiscal year 2010.
DOS actually calls it the Visa Waiver Program Adjusted Visa Refusal Rate, which equals to [Refusals minus Overcomes] divided by [Issuances plus Refusals minus Overcomes]. A 'refusal overcome' means a visa application is initially denied or rejected, but is later overcome when the applicant presents additional information, and a visa is subsequently issued.
For countries participating in the Visa Waiver Program (VWP), their citizens may visit the U.S. without visas. These VWP travelers are not included in the refusal rate calculations.