From an economic point of view, commodities have the following two properties. First, it is a commodity, usually produced and/or sold by many different companies or manufacturers. Second, the quality between production and sales companies is consistent. The difference between one person’s goods and another company is indistinguishable. This uniformity is called substitutability. Coal, gold, zinc and other raw materials are produced and classified according to uniform industry standards, which makes them easy to trade. Nevertheless, Levis jeans are not considered a commodity. Clothes, although used by everyone, are considered finished products rather than basic materials. Economists call it product differentiation. Not all raw materials are considered commodities. Unlike oil, natural gas is expensive and cannot be transported globally, making it difficult to price it globally. Instead, it usually trades on a regional basis. Diamonds are another example, and their quality varies too much to match the size required to be sold as classified commodities. It is believed that a commodity can also change over time. Onions were traded in American commodity markets until 1955, when New York farmer Vince Kosuga and his business partner Sam Siegel tried to monopolize the market. What was the result? Kosuga and Siegel flooded the market, earning millions of dollars, and consumers and producers were angry. In 1958, Congress passed the Onion Futures Act to outlaw onion futures trading. Like stocks and bonds, commodities are traded on the open market. In the United States, most transactions are conducted on the Chicago Board of Trade or the New York Mercantile Exchange, although some are also conducted on the stock market. These markets establish trading standards and measurement units for commodities, making them easy to trade. For example, the corn contract is 5,000 bushels of corn at a price of cents per bushel. Commodities are often called futures because they are not traded for immediate delivery, but for a later time, usually because it takes time to plant, harvest, extract and refine a commodity. For example, corn futures have four delivery dates: March, May, July, September or December. In the case of textbooks, goods are usually sold at marginal cost of production, but in the real world, prices may be higher due to tariffs and other trade barriers. The benefits of such transactions are to allow growers and producers to pay their money in advance, to give them liquidity to invest in their businesses, to make profits, to reduce debt, or to expand production. Buyers also like futures because they can use market declines to increase their holdings. Like the stock market, commodity markets are vulnerable to market instability. Commodity prices affect not only buyers and sellers, but also consumers. For example, higher crude oil prices may lead to higher gasoline prices, which in turn makes freight transportation more expensive.