Are there probably decent oil fields located in the middle of the ocean?
Are there probably decent oil fields located in the middle of the ocean?


tl;dr: no.

Hydrocarbon deposits form by thermal maturation (i.e. slow and mild heating) of buried organic matter (i.e. dead things) in sedimentary rocks. This is exactly why you find hydrocarbons...


  very near the country's shore, on the continental shelf


...because that's exactly where you find sedimentary rocks.

In contrast, the deep ocean basins are igneous rocks (mostly basalts) overlain by thin marine sediments with very little organic material. Whatever organic material is there, it never has the chance for maturation. It's either very cold, or gets heated in subduction and is lost forever in the deep mantle.