Not an easy question, at least for me. The uses of these documents seem to vary with the fields/industries, but LOG and LOU seem to be essentially the same-- a promise to pay-- while a LOI seems to be an assumption of responsibility, with the bottom line being paying if that responsibility fails. It seems to me that your choice may depend on the field you are speaking of, Vincent.


Here are some gleaned definitions/examples:


'There are many types of LOGs but the underlying purpose is the same for all, that being a guarantee of payment to a supplier.'


'In certain exporting countries, the government levy a heavy tax on drafts. In such a circumstance, the exporter may request the importer to specify in his/her letter of credit (L/C) application that "No drafts be issued". When the documents are presented to the negotiating bank, the bank issues a letter of undertaking indicating when and where the money will be paid, instead of accepting a draft drawn by the exporter. '


'Letter of Indemnity--

1. A letter guaranteeing that contractual provisions will be met, otherwise financial reparations will be made.

2. A letter requesting replacements for lost shares from a company's treasury. '