Civil conflicts within oil-rich states tend to last longer but are less likely to be mediated and end in a peace agreement. This implies that oil-funded conflict is less likely to end through a mediated settlement, despite offering a greater opportunity for peaceful resolution. This article builds on this puzzle, focusing on the following research question: to what extent does the presence of non-lootable natural resources impact on the onset and outcome of civil war mediation? I argue that oil wealth raises the relative capacity of the incumbent, making it more challenging for insurgents to force mediation and gain the guarantees against defection that are needed to resolve the problem of credible commitment. This theory is tested on 319 civil conflict episodes between 1946 and 2004. The results support the argument that non-lootable natural resources exert a strong negative effect on both the onset and outcome of mediation. The analysis also reveals that the negative effect of petroleum wealth increases relative to a state’s hydrocarbon revenue (per capita). This is an important contribution to conflict research focused on natural resources that has previously overlooked the relationship between resource wealth and civil conflict management efforts.