(eng): In this work, we are particularly focused on several sources of uncertainty in (pay-as-clear) electricity markets. To deal with stochastic demand we employ the so-called chance constrained formulations of the problem [1] of the ISO as well as the problem of each producer. In detail, the ISO minimizes the production cost using a value-at-risk (VaR) approach, thus hedging against discrepancies between estimated and real electricity demand. Similarly, in the day-ahead market, each producer is hedging against the uncertainty of his own prediction of the demand using VaR approach again. In such a setting we aim at determining the “best response” of a given producer, i.e. the bid maximizing its profit.