Why do some civil wars feature the mass killing of civilians while others do not? Recent research answers this question by adopting a ‘varieties of civil war’ approach that distinguishes between guerrilla and conventional civil wars. One particularly influential claim is that guerrilla wars feature more civilian victimization because mass killing is an attractive strategy for states attempting to eliminate the civilian support base of an insurgency. In this article, I suggest that there are two reasons to question this ‘draining the sea’ argument. First, the logic of ‘hearts and minds’ during guerrilla wars implies that protecting civilians – not killing them – is the key to success during counterinsurgency. Second, unpacking the nature of fighting in conventional wars gives compelling reasons to think that they could be particularly deadly for civilians caught in the war’s path. After deriving competing predictions on the relationship between civil war type and mass killing, I offer an empirical test by pairing a recently released dataset on the ‘technology of rebellion’ featured in civil wars with a more nuanced dataset of mass killing than those used in several previous studies. Contrary to the conventional wisdom, I find that mass killing onset is more likely to occur during conventional wars than during guerrilla wars.