A method of analyzing a fluid sample from a reservoir comprises: collecting the sample in a sampling container, wherein the sample container includes a sample receptacle, and wherein the step of collecting comprises allowing or causing the sample to flow into the sample receptacle; and determining at least one property of the sample, wherein the step of determining comprises using a multivariate optical element (MOE) calculation device, and wherein the step of determining is performed during the step of collecting and wherein the MOE calculation device is located at one end of the sample receptacle, or the step of determining is performed after the step of collecting. The sample is analyzed as the sample flows into the sample container or as the sample is being transferred from the sample container into a container.