In the preparation of miceller systems for enhanced hydrocarbon recovery, surfactants are used which consist of N-acyl N-alkyl-.alpha.-amino-carboxylic compounds. The considered products comply with the general formulas: ##STR1## wherein at least one of R.sup.1, R.sup.2 and R.sup.3 is a saturated or unsaturated C.sub.1 -C.sub.22 aliphatic hydrocarbon radical (one of them having optionally a carboxylic group) the other or others being a hydrogen atom, R.sup.1, R.sup.2 and R.sup.3 having together from 4 to 22 carbon atoms, R.sup.4 is an alkyl radical of 1-5 carbon atoms, R.sup.5 an alkyl radical of 1-12 carbon atoms and M is an alkali or alkaline-earth metal, ammonium or a quaternary ammonium group.As used in the formation of micellar systems (aqueous solutions, emulsions or mirco-emulsions) for enhanced oil recovery, these surfactants have improved performances, particularly, in field waters of high polyvalent ion (Ca.sup.++ and Mg.sup.++) content, within relatively wide temperature and pH ranges.