As contained in the "application instruction" document (see http://travel.state.gov/pdf/DV_2015_Instructions.pdf), Nigerians are not eligible to apply for the 2015 programme. Apparently, more than 50,000 Nigerians immigrated to the US in the previous 5 years.

Here's an excerpt:

For DV-2015, natives of the following countries are not eligible to apply, because more than 50,000 natives of these countries immigrated to the United States in the previous five years:
Bangladesh, Brazil, Canada, China (mainland-born), Colombia, Dominican Republic, Ecuador, El Salvador, Haiti, India, Jamaica, Mexico, Nigeria, Pakistan, Peru, Philippines, South Korea, United Kingdom (except Northern Ireland) and its dependent territories, and Vietnam.

Persons born in Hong Kong SAR, Macau SAR, and Taiwan are eligible.

Changes in eligibility this year:
For DV - 2015, natives of Nigeria are no longer eligible.

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