I am certainly not more knowledgeable but I did look it up just...

I am certainly not more knowledgeable but I did look it up just after the Erin announcement.
The best answer I found was GeoExpro magazine :
http://www.geoexpro.com/articles/2016/06/the-gambia-the-next-major-oil-play

Exploration for hydrocarbons in The Gambia dates back to the 1950s, but none of the companies involved in the early exploration of the area progressed beyond initial studies apart from Chevron, who drilled Jammah-1 in 1979. This is located in Block A2 and to date is the only well drilled offshore The Gambia. It was plugged and abandoned with gas shows at a TD of 3,020m. It targeted an Albian shelf-edge carbonate feature slightly to the east of the axis of a large north-south trending anticline and encountered viable sandstone and carbonate reservoir horizons but only minor petroleum shows. The well was drilled on the basis of 2D seismic data and post-well studies suggested it was dry due to erosion of potential Turonian source rocks at the location, though analysis of the new seismic data acquired by Polarcus in 2015 suggests it did not test a valid structural closure.

Studies have reviewed the offshore exploration potential and a range of play types including fan and slope channel systems, karstified reef build-ups, 4-way closures and clastic deposits onlapping the shelf edge have been identified. No further drilling has taken place offshore The Gambia.