March 25 (Reuters) - Loading of Venezuela's heavy crude

at its main oil ports slowed this week after the administration

of U.S. President Donald Trump published an executive order

imposing a 25% tariff on trade with countries buying the South

American nation's oil, according to shipping data and a company

document.

The termination of a key license for Chevron ( CVX ) to

operate in Venezuela in late May also has reduced the number of

vessels chartered by the company waiting to load in Venezuelan

waters, the data showed.