EDT's v.s EDP's

The two most common concentrations used in the fragrance industry are Eau de Toilette and Eau de Parfum.
EDT's contain anywhere from 8% fragrance oils to 15% oils where as EDP's generally contain between 16% and 25% oils in relation to the carrier agent which is usually alcohol.

Many fragrances come in both concentrations but which one to choose is often not a straight forward decision as both variants can differ greatly both in scent and performance and especially cost!

Below i would like to highlight both the pros and cons of both EDT's and EDP's, all in my own opinion of course.

Lets starts with EDT, these contain a lower concentration of perfume oils so therefor have a higher percentage of alcohol. This generally mean that projection and sillage are often better but they can lack the longevity of an EDP.
This is not always the case though as there are some EDT's that perform extremely well in all departments, the main reason for the potential lack of longevity is down to the ingredients used and the concentration, as alcohol evaporates it takes the scents molecules with it and body heat helps this process. EDT's will burn of the skin at a much higher rate than EDP's.  
EDP's on the other hand with there higher concentration of oils leave a residue on the skin, this oil often takes a fair while to evaporate away resulting better longevity. EDP's are often denser than EDT's and are more complex and of a richer nature and can and do often smell different to the EDT equivalent. Where as EDT's sometimes have better projection and sillage EDP's have better longevity due to them remaining on the skin for longer.  
I personally believe that EDP's are better for people who have  drier skin as lighter fragrances tend to have longevity issues on such skin types as they are less oily, EDP's are better in this instance.

EDP's tend to generally be more expensive than EDT's because of the higher concentration so hence they cost more to produce, the price can vary greatly from a few pounds to quite a bit more.

This is just my take on the subject, i hope you enjoyed reading and please fell free to comment!

Midnight in Paris by Van Cleef and Arpels

EDT on the left and EDP on the right