Believe it depends on the country that he has his passport from....

Visa on arrival is available for the residents of these countries:

Andorra, Australia, Austria, Belgium, Brunei, Canada, Denmark, Finland, France, Germany, Greece, Hong Kong, Iceland, Ireland, Italy, Japan, Liechtenstein, Luxemburg, Malaysia, Monaco, New Zealand, Norway, Portugal, San Marino, Spain, Sweden, Singapore, South Korea, Switzerland, The Netherlands, USA, UK, Vatican City.