An apparatus to simulate biocide performance in crude oil pipeline conditions is disclosed. The apparatus includes: a reactor to simulate a two-phase crude oil pipeline which includes a crude oil phase above a water phase. The reactor has an agitator to control a flow of the water phase in the reactor in response to a motor that drives an agitation rate of the agitator. A crude oil inlet supplies crude oil to the reactor for the crude oil phase. A water inlet supplies water to the reactor for the water phase. A control circuit is configured by code to control a proportion of the water to the crude oil supplied to the reactor and to control the motor to drive a desired agitation rate of the agitator. A biocide inlet supplies biocide to the reactor. A water sample outlet enables sampling of the water phase of the reactor.