The refiner had initially asked for more Saudi oil after the world's top exporter slashed prices for April-loading supplies, the sources said.

However, freight rates for oil tankers surged and offset the large discounts on Saudi oil, making it less economical, they said.

Also, Saudi Aramco was offering more light crude while Unipec's preference was for medium and heavier grades, two of the sources said.

Sinopec declined to comment.

(Reporting by Florence Tan and Shu Zhang; Editing by Shri Navaratnam and Clarence Fernandez)