If you are looking for a reliable taxi while in Libreville, you may want to consider hiring Simon. I used him for two long trips (I met him by chance at the airport, so I have no other connection to him).
Very honest and diligent. Fun also. He came directly from his home to drive me to the airport very late one night. Next time I am in Libreville, I will call him in advance for airport pick up.
You can call him in advance for any pre-arranged trips.
Tel. for Simon in Libreville:
(+241) (0)7 35 6915 or
(+241) (0) 3 27 6056