Exclusive: PDVSA changes oil deals to include shipping as sanctions bite - documents

The United States has blacklisted vessel owners, shipping operators and threatened to sanction any tanker facilitating the country's oil exports as it tightens restrictions on trade with the South American country.Washington has been trying to weaken socialist President Nicolas Maduro by choking the OPEC member's oil exports, depriving the government of petrodollars -- its main source of revenue.Most shipping firms are avoiding Venezuela because of the sanctions, making it difficult and expensiv