Balancing energy markets and imbalance mechanisms are pressing issues to provide flexibility for the electricity system to enable an efficient integration of volatile renewable energies. Because of the need for flexibility and shortterm (generation or demand) reaction to forecast errors of renewable generation, liquidity and market volume of short-term markets have significantly increased. In Austria, the balance responsible parties play a role for short-term electricity flexibility, because it is possible to use the flexibility of a balance responsible party to optimize the portfolio and additionally to support the system.