We present an algebraic model for the description of concurrent systems with capabilities to express timed and probabilistic behaviours, as well as urgent interactions. This model is based on basic LOTOS, including a probabilistic choice operator, a timed prefix operator for the specification of time intervals where the involved actions are enabled, and a prefix operator for the specification of urgent interactions. An operational semantics for this model is also presented, which is based on the execution of bags. This semantics establishes that processes must always execute as many urgent actions as they can, thus complying in a great extent with the user specifications of urgent actions.