Methods according to the invention include providing an OFA tool which subjects formation fluids to NIR illumination and which provides a spectral measurement of peaks at about 6,000 cm.sup.-1 and about 5,800 cm.sup.-1. The methods according to the invention also include calculating a ratio of the amplitudes of the absorption peaks to determine GOR. According to an alternate embodiment, the methods of calculating the ratio include referring to a database of spectra of hydrocarbons found in formation fluid and adjusting the amplitudes of the methane and oil peaks to account for the influences of other hydrocarbons on the spectrum of the formation fluid. A borehole apparatus for measuring the spectral peaks of oil and methane includes a testing region, a conduit for directing formation fluid into the testing region, a light source emitting at least near infrared rays into the testing region, a spectral detector optically coupled to the testing region, and a processor coupled to the spectral detector. The testing region is a transparent tube or chamber which is located between the light source and the spectral detector such that light directed from the light source to the spectral detector is interrupted by formation fluid. The spectral detector is preferably a filter spectrograph which measures the spectrum of the light which has been transmitted through the formation fluid in the testing region.