A private electronic market (PEM) uses the Internet to connect a limited number or pre-qualified buyers or sellers in one market. PEMs are a hybrid between perfectly open markets (e.g. exchanges where there is no pre-existing relationship between buyer and seller - similar to eBay) and closed contract negotiations (such as a sealed bid tender, where there is no visibility between competitors and hence no response to competition). The core idea of PEMs is to create competition among buyers/sellers while allowing buyers/sellers to adjust all those aspects of the deal that are typically only dealt with in a negotiation. This creates a problem of "comparing apples and oranges": bids may be quite different in many dimensions and therefore cannot easily be compared. Apart from the dimension of price these could include pre-negotiated discounts (e.g. for loyalty), specific qualities, combinations of goods and services with conditional pricing, freight differentials, contract fulfillment timing, payment terms, or deliberate constraints such as market share limits.