Nationals from Cameroon, Central African Republic, Republic of Congo, Chad, Equatorial Guinea, Mauritius, Morocco, South Africa and Tunisia Van enter for up to 90 days without a visa.
An evisa is available for everyone else and costs 70 Euro.
Australia, Austria, Argentina, Bahrain, Belgium, Brazil, Bulgaria, Canada, China, Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, India, Indonesia, Ireland, Italy, Japan, Kuwait, Latvia, Lithuania, Luxembourg, Malta, Mexico, Netherlands, Oman, Poland, Portugal, Qatar, Romania, Russia, Saudi Arabia, Slovakia, Slovenia, South Korea, Spain, Sweden, Turkey, United Arab Enirates, United Kingdom and United States can obtain a visa on arrival.
Gabon eVisa - official site
Gabon embassies worldwide
Gabon visa on arrival