Workplaces in the oil and gas (O&G) industry have evolved to become part of the modern complex sociotechnical system that characterises onshore and offshore facilities today. The intense interactions between workers, systems, equipment and processes have made companies in this sector more productive. However, significant and complex risks have also emerged. Managing them requires a methodology capable of understanding and recognising how this entire sociotechnical system works. This research uses the FRAM to model the activities performed by drillers, from the perspective of their workplace, inside the drilling unit of an offshore oil rig—a complex sociotechnical system. The interviews, on-board observations and data gathering performed as part of this study provided information that was used to build a FRAM model capable of representing the real work done by drillers inside the doghouses on offshore oil rigs. Through this model, the variability of human behaviour could be analysed in the context of the different situations that may happen, enabling researchers to understand the specific demands of the work and the correlation between WAI and WAD that naturally emerges. This FRAM-based analysis acknowledges that human factors and non-technical skills are responsible for the productive and safe execution of the work in both normal and critical operations situations, and identifies the impact of this variability—positive or negative—in the execution of daily tasks. It shows that workers’ varied responses can properly deal with complex system demands both in normal situations and in emergencies.