Users will often want to calculate odds for a variety of combinations of events to establish a favourable/desired amount of risk in order to place a wager. Regrettably, odds produced by bookmakers often change with sufficient frequency that it is not possible for a user to calculate all the possible odds for a variety of combinations of events before the odds produced by a bookmaker change, thus invalidating their calculations. The invention provides a computer system for enabling placement of wagers that calculates a plurality of combined odds, each of the combined odds comprising a combination of events with corresponding selected outcome types. In this way, users may place combination wagers on the outcomes of a combination of events in an informed manner; that is, being aware of the combined odds and alternative combined odds available.