I believe they are part owners in three offshore platforms but they are primarily a US refining and distribution (retail) company.
2007 Annual Report
http://www.valero.com/NR/rdonlyres/D105445B-CC29-413C-99B5-C768FDF6E151/0/VLOARFINALFORWEB.pdf
See Page 17
If they have to purchase most of their crude, they are in a tough business position. I wouldn’t build a refinery these days unless I had enough crude production already to feed the plant.