A base time is decided, say 15 minutes. Then each player submits a written private bid of how little time they are willing to accept as black. Whichever bid is lower will play black, using that amount of time. The white player gets the base time (his bid is not relevant). White must win the game, otherwise black is the winner of the armageddon and the match.

A base time for the game is predetermined, say 15 minutes. Then each player submits a single written private bid of how little time they are willing to accept as black. Whichever bid is lower will play black, using that amount of time. The white player gets the base time (his bid is not relevant). White must win the game, otherwise black is the winner of the armageddon and the match.

An alternative would be an open auction with decreasing bids until one player declines to bid lower. The private bidding is currently considered simpler and cleaner, though either method would work.