Dirion's Magical Vault:

While this spell is active, the caster may choose to increase the storage capacity of any resource including money during a session. For each resource that has its storage increased by 5 ($250 per era, for money), this spell gains +1 upkeep. For example, if Wood has +10 storage capacity, Stone has +5 storage capacity, and Mounts also has +5 storage capacity, this spell has a 4 upkeep. Once a storage has been increased, it cannot be decreased without dropping the spell. You pay the upkeep, even if none of the storage ends up actually being used. If this spell ends, all the resources that go over the capacity is destroyed automatically. If the spell is dispelled, the aforementioned affect occurs, with 25% of all the lost resources going automatically to the dispeller. The maximum storage that can be created is twice the base storage.