Nowadays, to hear many of the oil sellers and operators, particularly their brokers and agents, who are involved in the international open market crude selling, describe it, this document _ called the "Letter of Intent" or LOI, for short _ is not only an essential document for doing crude oil business, but one which every credible person or company engaged in crude buying should always use in initiating a purchase. To many of these operators, not only should crude oil buyers use the LOI to initiate their buying orders, but initiating the purchase order in that manner, they say, has always been the usual way by which credible buyers initiate their purchasing projects, as doing it that way indicates, they claim, that a buyer is "serious" and genuinely committed to making a purchase.
If what you want is a quotation or offer, then sending a letter of intent makes you look ignorant while requesting a quotation will generally at least make you look like you know what it is that you want. And what you want, after all, is a price quote. Hence you want to request a price quote, via a request for quotation.