To be more specific, recent, sizable discoveries of it in the North Cuba Basin _ deep-water fields that have already drawn the interest of companies from China, India, Norway, Spain, Canada, Venezuela and Brazil.

[...]

Musings from  Crooked Timber:

[...] Some possibilities:

1. Suddenly realize that the embargo isn't working and end it;
   
2. Suddenly realize that the embargo isn't working where oil is concerned - end it for oil, but keep it in place for everything else.
   
3. Dispute Cuba's territorial claims where the oil was found;
   
4. Escalate - either blockade or at least stop suspending enforcement of title III the Helms-Burton amendment [pdf] until Cuba is a democracy like Saudi Arabia;
   
5. Really escalate - invade Cuba (beyond Guantanamo Bay) or some other country, related or not - I'm thinking Venezuela;
   
6. Keep very quiet about this and hope Castro dies soon and declare success no matter what the replacement regime looks like.
   

[...]

I don't know if the quantities are interesting in the global picture, from the Washington Post:

Seven months later, a report by the U.S. Geological Survey confirmed it: The North Cuba Basin held a substantial quantity of oil _ 4.6 billion to 9.3 billion barrels of crude and 9.8 trillion to 21.8 trillion cubic feet of natural gas. Cuba wasted no time, dividing the 74,000 square mile (120,000 square kilometer) area into 59 exploration blocks, and then welcoming foreign oil conglomerates with offers of production-sharing agreements.

With gas a 7 dollar per thousand cubic feet and oil at 70 per barrel, taking median estimate, it sums to 630 billion dollars. Cuba has a GDP of 33 billion dollars a year.