Wen Tao,
if you really are serious about investing your money in SEY you should take time out to read the announcements they have made over the past 12 months.
of particular interest is the interim results and the recent operational update.
in simple terms, the letter of credit is basically providing the Mauretanian Government with a loan for them to buy in to 12% of the revenues flowing from the Chinguetti oilfield.
in return, SEY get a significant percentage of the Govt's share of the revenue with the loan likely to be repaid to SEY in 2007.