OVERVIEW OF THE STUDYOver the past decade, supply chain management has had an influence on businesses around the world. Purchasing is a supply chain function that becomes the most important element in establishing value-added products or services. The major aspect of purchasing is the selection of suppliers. It is recognized that selecting an appropriate supplier is one of the key success factors of a business. Choosing the right supplier is always a difficult task for the purchasing manager (Liu et al., 2005). The right selection of suppliers can lead the business to success and achieve goals. On the contrary, poor selection of suppliers can lead the company to financial problems. Therefore, purchasing departments should emphasize on supplier performance evaluation which is not only concerned with one criterion such as price, but also take into account several supplier evaluation criteria in order to select the right one. supplier. 1.1 Background of the Study Nowadays, the oil and gas industry plays an important role. major role in driving the business locally and globally. It provides essential energy and chemicals to industry, homes and transportation, which are increasingly consumed by users every day. There are around fifty oil and gas companies established in Thailand and ten out of fifty are ABC company customers. ABC Company is one of the leading traders, stockists, exclusive distributors and engineering companies supplying industrial process equipment of piping materials, e.g. pipelines, flanges and fittings. The company was established in May 1998 with a 100% Thai shareholder. The company provides materials and supplies to the oil and gas industry to construct and maintain transportation pipeline projects and shutdown plants. the amount is also constantly increased by 11.87%. The increase in purchases comes from the company which undertakes to stock the material in order to supply it at any time when the customer needs it to satisfy his satisfaction. Table 1.1 shows the comparison of sales data and purchase data from 2012 to 2013 of ABC Company. Total purchases (million THB) 438,490 11.87% (approximately 52 million THB) Source: ABC Company During the year, ABC Company needs to purchase piping materials consisting of pipes, flanges and fittings in the proportion shown in Figure 1.2. Figure 1.2: Purchase proportion of Company ABC Source: Company ABC Source: Company ABC According to Figure 1.2, the amount of purchases of Company ABC from 2012 to 2013 for pipelines, flanges and fittings is approximately equal at 68%, 18% and 14% respectively..