A conceptual framework is provided by which a unified quantitative Fourier transform infrared (FTIR) methodology for the determination of acid number (AN), base number (BN) and moisture (H₂O) of in-service lubricants can be achieved. It is based on stoichiometric reactions designed to produce CO₂; an IR spectrally active reaction product made common to the three methods to facilitate quantification. This originated from the reaction of toluene isothiocyanate with H₂O to produce CO₂ for moisture determination in oils, that can also be achieved by the addition of acid to oils containing over-based detergents to determine BN, and the use of a defined, certified over-based detergent standard to react with acids present in the lubricant to determine AN. CO₂ has a very strong, sharp IR absorption at 2335 cm^-1 where few competing interfering organic substances absorb, and being  hydrophobic, makes it a suitable end product to measure spectrally in solvent-diluted oils and lubricants. This approach is contrasted with current AN/BN FTIR methods in terms of chemistry, basic spectroscopy and anticipated performance. A basic FTIR configuration, sample preparation procedures and a method-common calibration/analytical protocol for the three methods is presented for the analysis of in-service lubricants. All use a reagent-diluent to facilitate reactions in septum-capped vials to contain and equilibrate the CO₂ produced and reduce oil viscosity to facilitate sample handling. Loading is by needle septum penetration and aspiration, manually or via autosampler, with the same physical FTIR configuration used for all methods. As structured, the FTIR methodology proposed could provide an efficient, cost effective and environmentally sound means of obtaining ASTM-similar titrimetric results for AN, BN and H₂O for in-service oils at rates ranging from 20 (manual) to 180 (autosampler) samples per hour for pre-prepared samples.