Disclosed herein is a method of reducing the vapor pressure of a processed crude oil, wherein such vapor pressure reduction is sufficient to allow safe transportation of the oil. After high-pressure processing for off gassing and subsequent low-pressure separation of water, a processed crude oil may still have sufficient vapor pressure to create hazardous conditions if the oil is transported. This disclosure reports that as little as 10 ppb of certain siloxane polymers applied to such processed crude oils results in treated oils with reduced vapor pressure. Vapor pressure reduction is typically about 1 psi to 10 psi after the application of the disclosed siloxane polymers.