Recently, research has focused on processing tasks that require continuous execution to produce data in a real-time manner. Such tasks often also need to be executed for long periods of time such as years, requiring large amounts of resources (e.g. CPUs) that can be found in a Grid. However, a Grid may be unwilling or unable to allocate resources for continuous usage far in advance, because of high fluctuations in resource availability and/or resource demand. Therefore, a client must relax its requirements in terms of long-term execution, and negotiate a shorter period of execution time; when this period ends, the client must negotiate again to continue task's execution. We propose a negotiation strategy, ConTask, which helps to increase the periods of execution time, and reduce the length of interruptions between them.