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At least 34 U.S.-sanctioned oil tankers with a history of carrying Venezuelan oil are currently at sea in the Caribbean, according to a new analysis obtained by CNBC on Wednesday.

And at least 12 of those tankers appear to be filled with crude oil from Venezuela, according to vessel location data from Kpler, a global trade intelligence company.

One of the tankers, Skipper, was seized by the U.S. forces in the Caribbean last week and was being taken to the United States.