The following countries can obtain a visa on arrival for free All EU countries, Benin, Brazil, Burkina Faso, Canada, Cape Verde, Central African Republic, Chad, China, Congo, Côte d'Ivoire, Djibouti, Gambia, Ghana, Guinea, Guinea-Bissau, India, Japan, Liberia, Malaysia, Mali, Mauritania, Mauritius, Morocco, Niger, Nigeria, Sierra Leone, Singapore, South Korea, Togo, Tunisia, United Kingdom and United States.
A visa on arrival is available for almost everyone else, you might want check as details change frequently.
Visa information for Senegal
Senegal Embassies