Abstract: A system and method to distribute computation for an exchange in which advertisers buy online advertising space from publishers. The exchange maintains submarkets, each containing a subset of the ad calls supplied by publishers and a subset of the offers and budgets representing demand from advertisers. Portfolio optimization techniques allocate the supply of ad calls from publishers over the submarkets, with the goal of maximizing profits for publishers while limiting the volatility of those profits. Portfolio optimization techniques allocate the demand from advertisers over the submarkets, with the goal of maximizing return on investment for advertisers. The exchange re-allocates supply and demand over submarkets periodically. Also, periodically, the most effective submarkets are replicated and the least effective submarkets are eliminated.