No specific meaning is attached to these letters. The in between missing letters were believed to have another meaning or perceived to be too easily confused.

For example the December 2007 Crude Oil Futures is - CLZ7, where the letter Z represents the month of delivery. See below.

(F=Jan, G=Feb, H=Mar, J=Apr, K=May, M=June, N=July, Q=Aug, U=Sep, V=Oct, X=Nov, Z=Dec)

How were these letters determined for each month? Is there a particular idea behind the derivation of these letters?