All stocks are affected in a way by the Brexit. Because investors are willing to invest less in a uncertain stockmarket. Other investors are taking out their money because they want to avoid losses. So a pullback is normal and expected in this case.
I don't expect Valero to lose money due to less business with UK, however I don't know how much they are in business with the UK. But judging from yesterday's trading I don't think it will be much. If they did the pullback would be larger.
Off a bigger concern is what the Brexit might do to the economy. If a lot of companies suffer losses, the economy might too and then so will energy market and with that VLO.
So how much the Brexit will affect VLO is very uncertain. But for sure there will be an effect.
Market Data 
Markets 
AI
