The authors propose that a reciprocal resource gain spiral forms between coworker-based perceived social support and trust, which leads to coworkers investing personal resources into each other across work days. The authors extend conservation of resources theory by differentiating between resource investment behaviors, the perceived availability of resources, and perceptions about investment instrumentality while also examining accumulation effects that have been previously untested in studies of gain spirals. The authors confirm their hypotheses with data collected over five working days from 177 pairs of coworkers (employee N = 354) working across a wide range of jobs and industries. The authors also offer practical implications of this spiral, limitations of this research, and future directions for research on conservation of resources theory, resource investment, and day-level studies of employee behaviors.