Methods and related systems are described for analyzing phase properties in a microfluidic device. A fluid is introduced under pressure into microchannel, and phase states of the fluid are optically detected at a number of locations along the microchannel. Gas and liquid phases of the fluid are distinguished based on a plurality of digital images of the fluid in the microchannel. Bi-level images can be generated based on the digital images, and the fraction of liquid or gas in the fluid can be estimated versus pressure based on the bi-level images. Properties such as bubble point values and/or a phase volume distribution ratio versus pressure for the fluid are can be estimated based on the detected phase states of the fluid.