A reliable and credible system to ensure bids are handled confidentially is important, to prevent any opportunity for bid-tampering, and to protect commercially sensitive information in bids.
Often bids are delivered in hard copy in sealed envelopes. Typically financial and technical bids are delivered in separate envelopes-financial bids are only opened for bidders that pass the technical assessment, and are often opened publicly to avoid any possibility of bid tampering. For example, the Philippines BOT law rules and regulations set out a two-envelope system for receiving bids [#202, Rule 7]. The World Bank sample bidding documents for output- and performance-based road contracts [#275, pages 19-21] also describe a sealed-envelope bid system, but allow for use of an electronic sealed bid system as an alternative. One advantage of an electronic system is that it prevents bidders from monitoring or interfering with physical bid delivery.
Dumol's diary of the Manila Water privatization by concession [#63, pages 85-98] includes a detailed description of the process for bid submission and bid opening in practice.