Visas are required for all with the exception of Americans, though many embassies outside the country are not always aware of this exemption, and officers on the ground will be suspicious.
Visas can be purchased in neighbouring countries for up to US$70. Obtaining a visa can be a long process and may require having an invitation from an organisation in the country. Expect many trips and long waits.
Visas for onward travel
Visas for Cameroon and Gabon are available from embassies in Malabo. Equatorial Guinea is one of the best places to get a Gabonese visa: 30-day visas cost US$60 and take about three days to process. Three-month visas for Cameroon cost US$50 and are generally issued the same day. Visas to Cameroon are available at all border crossings.