There are two types of cabs that operates in Ouaga. The cheaper ones are the taxi vert, (small green cabs) which ply fixed routes throughout the city, usually to and from La Grande Marché, the busy large central market. Fares are fixed at around 500cfa, but at night be prepared to negotiate before boarding as the fare is jerked up.
Be ready to share the taxi with other passengers going your direction, sometimes four people get squeezed into the back seat. If you decide to make the cab private, the fare will definitely shoot up.
The second type of cabs are the yellow ones (taxi jaune). They are metered, more reliable and offer door to door services, but are definitely more expensive, and you won’t have to share with anyone.