The invention relates to a method of extracting hydrocarbons from a subterranean formation, comprising: - injecting a surfactant composition into the subterranean formation, and - collecting hydrocarbons displaced by the injected surfactant composition; wherein the surfactant composition comprises at least one surfactant compound of formula (I): wherein x is an integer from 0 to 3, R1, R2, R3, R4 and each R are independently a hydrogen atom or an alkyl group, each A is an alkylene group, and the total number of carbon atoms in the surfactant compound of formula (I) is from 10 to 21. The invention also relates to a composition comprising liquid or supercritical carbon dioxide and at least one surfactant compound of formula (I).
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