It was suggested that 2 preconditions promote proactive control: a pending plan to control performance and availability of working memory (WM) storage resources. In 4 experiments, we applied these preconditions to the Stroop task. Using a new approach, we focused on task conflict while manipulating not only the different stimuli proportions, but also participants' expectations (experience with or without incongruent trials in practice), external cues (experimental break), and WM load. In Experiment 1, we found that preexperimental exposure to incongruent stimuli triggered proactive control, resulting in a negative facilitation effect. However, once the first experimental block ended, indicating the end of the episode requiring control, proactive control ended. A regular facilitation emerged, supporting the idea that proactive control occurs for well-defined control episodes (Experiments 1 and 2). In Experiment 3, we found that applying proactive control in the Stroop task requires availability of WM resources and when such resources are limited, no control is applied and regular (rather than negative) facilitation is found. These results were replicated in Experiment 4. Therefore, it appears that experiencing incongruent trials is essential but not sufficient to recruit proactive control; available WM resources are also needed. These findings, specifying the importance of preconditions for proactive control, were replicated in Experiment 4. The current study enhances our understanding of conflict monitoring and allows us to examine the common conflict monitoring models from a different point of view.