An interesting article made by Dr Thomas Chaize :

In english : http://www.dani2989.com/pdf/7oil1108gb.pdf

In french : http://www.dani2989.com/pdf/7oil1108fr.pdf

In spanish : http://www.dani2989.com/pdf/7oil1108es.pdf

In italian : http://www.dani2989.com/pdf/7oil1108it.pdf

In german : http://www.dani2989.com/pdf/7oil1108de.pdf

In portuguese : http://www.dani2989.com/pdf/7oil1108pt.pdf