Abstract: A liquid sample container system is for receiving and protecting a liquid sample including oil obtained from a surface of a large liquid source having at least a thin layer of oil thereon. A cylindrical jar of the container system has a bottom, an open top and a height therebetween. The jar has an uncontaminated interior for receiving the liquid sample therein by gravity toward the bottom. The jar has threads about the open top. The jar lid has an inside and matching threads for being threadably received on the threads of the jar for sealing the interior thereof. A lid insert has an outer surface of polytetrafluoethylene to which oil tends to temporarily adhere. The lid insert has a disc portion located within the inside of the jar lid for being disposed over the open top when the jar lid is threadably installed on the jar.