Compositions and methods and uses relating thereto

A method of reducing the viscosity of a crude oil having a basic sediment and water (BS&w) content of less than 10% by volume, the method comprising:

• adding to the crude oil (i) a surfactant compound including at least two hydrophobic groups of formula (I);
• wherein each R is an optionally substituted hydrocarbyl group baying from 2 to 16 carbon atoms and M+ is a hydrogen ion, an ammonium ion or a metal ion;
• and (ii) an oxyalkylated phenolic resin;
• wherein
• the resultant mixture has a water content of less than 10 vol %.