which has led to more accurate estimates of bid prices. Bid prices represent the minimum price a seller should accept for a single piece of inventory and are popular control mechanisms for Hotels and Car Rental firms. Models derived from developments in financial engineering are intriguing but have been unstable and difficult to place the parameters in practice. Yield management tends to focus on environments that are less rational than the financial markets. Yield management system Firms that engage in yield management usually use computer yield management systems to do so. The Internet has greatly facilitated this process. Enterprises that use yield management periodically review transactions for goods or services already supplied and for goods or services to be supplied in the future. They may also review information (including statistics) about events (known future events such as holidays, or unexpected past events such as terrorist attacks), competitive information (including prices), seasonal patterns, and other pertinent factors that affect sales. The models attempt to forecast total demand for all products/services they provide, by market segment and price point. Since total demand normally exceeds what the particular firm can produce in that period, the models attempt to optimize the firm's outputs to maximize revenue. The optimization attempts to answer the question: "Given our operating constraints, what is the best mix of products and/or services for us to produce and sell in the period, and at what prices, to generate the highest expected revenue?" Optimization can help the firm adjust prices and to allocate capacity among market segments to maximize expected revenues. This can be done at different levels of detail: by goods (such as a seat on a flight or a seat at an opera production) by group of goods (such as the entire opera house or all the seats on a flight) by market (such as sales from Seattle and Minneapolis for a flight going Seattle-Minneapolis-Boston) overall (on all the routes an airline flies, or all the seats during an opera production season) Yield management is particularly suitable when selling perishable products, i.e. goods that become unsellable at a point in time (for example air tickets just after a flight takes off). Industries that use yield management include airlines, hotels, stadiums and other venues with a fixed number of seats, and advertising. With an advance forecast of demand and pricing flexibility, buyers will self-sort based on their price sensitivity (using more