It is very unlikely that Valero would announce selling Aruba if there were not some offers already on the table or parties interested in the Refinery. Lot of oil producers looking to invest in refining assets and existing assets are easier to do than Greenfield.
Trying to guess “who” isnt a good use time – rumors can often have element of truth but more often are “off-the-wall”.
Petrobras is good potential but they arleady have lot expansion going on in Brazil Refineries, new Upgrader JV with PdVSA & the Houston Refinery to rework for Brazil Heavy Crude slate. Similar can be said for COP – has expansions at Billings, Borger & Woodriver (with versions II waiting when current EPC comes online), plus the new Canada JV Bitumen Crude to feed them, and the Ferndale Refinery is on Hold / not cancled.
Marathon would be another good canidate – but they have been slow getting out of acquisition gate since they bought their way free from USX.