The Los Bajos fault, of late Miocene or Pliocene age, cuts across the southwestern peninsula of Trinidad with a strike of about N. 70° W. from Point Ligoure on the western coast to the vicinity of Negra Point on the southern coast. In its western part the apparent downthrow is more than 10,000 feet toward the south and in its eastern part there is an apparent downthrow of 7,000 feet toward the north. The writer believes this fault to be essentially a strike-slip fault with the northern side moving eastward relative to the southern side and the apparent throw at the fault line resulting from the discordant juxtaposition along the fault of folded structures developed previous to and during the fault movement. In the western part of its course the differential horizonta movement amounts to as much as 7 miles. The fault has played a major role in influencing the migration and accumulation of oil and its course intersects several major oil fields. The origin of this fault is explained by the writer as due either to (1) "gravity collapse" of incompetent sedimentary filling of the Orinoco basin, or (2) crustal adjustment related to drift movement of the American continents.